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■ft 



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(THEORy <;nf ColouA). 



Absorption Spectra. Frontispiece. 



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COLOUR 



A HANPBOOK OF THE THEORY OF 

COLOUR 

GEOKGE H. HURST, RC.S. 



SECOND EDITION, BE VIS ED 

BY 

H. B. STOCKS, F.I.C., F.C.S. 



WITH ELEVEN COLOURED PLATES AND SEVENTY-TWO 
ILLUSTRATIONS AND DIAGRAMS 



LONDON 

SCOTT, GREENWOOD & SON 

8 BROADWAY, LUDGATE, E.G. 

1916 

[All lights remain with Scott^ (rveenwood <t' >%n] 

D. VAN NOSTRAND COMPANY 
NBW YORK 



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U 



First Edition 1900 

Second Edition, Revised . . January, 1916 



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PREFACE. 

The subject of colour is one of considerable inter- 
est, more especially to artists, painters, dyers, calico 
printers, and others who use colour or colours in 
their everyday work. Such persons have consider- 
able practical experience in the mixing and appli- 
cation of colours for various purposes — painting, 
dyeing and printing of textile fabrics, etc. — but they 
will no doiibt have met with, from time to time, 
curious effects of mixing the various colours together. 
To such persons a knowledge of the theory of colour, 
its cause and production, and a succinct account 
of the phenomena which occur on mixing colours to- 
gether in various ways, will be of interest. In the fol- 
lowing pages it has been the author's endeavour to 
present such matters as clearly as possible, and, while 
keeping in mind the latest investigations in the field 
of colour, particular attention has been paid to the 
requirements of the practical man, an explanation 
being given of the results which are obtained by mix- 
ing various dyes and pigments together, phenomena 
which occur every day to the dyer and painter. 

ill 

371694 

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IV PllEFACfi. 

In the compilation of this book the author has 
received much valuable information on the subject 
from the manuals of Chevreul, Benson, Rood, Church, 
and others, and to these he begs to make due ac- 
knowledgment. 

H. B. STOCKS. 

November^ 1916. 



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CONTENTS. 

CHAPTER I. 
COIiOUR AND ITS PRODUCTIONS. 

Light — Colour — Dispersion of White Light — Methods of Producing the 
Spectrum — Glass Prism and Diffraction Grating Spectroscopes — The 
Spectrum — Wave Motion of Light —Recomposition of White Light — 
Hue — Luminosity — Purity of Colours — The Polariscope — Phosphores- 
cence — Fluorescence — Interference Pages 1-31 

CHAPTER IL 
CAUSE OF COLOUR IN COLOURED BODIES. 

Transmitted Colours — Absorption Spectra of Colouring Matters. Pages 32-64 

CHAPTER III. 
COLOUR PHENOMENA AND THEORIES. 

Mixing Colours — White Light from Coloured Lights— Effect of Coloured 
Light o^ Colours — Complementary Colours — Young-Helmholtz Theory — 
Brewster Theory — Supplementary Colours — Maxwell's Theory — Colour 
Photography Pages 55-90 

CHAPTER IV. 
THE PHYSIOLOGY OF LIGHT. 

Structure .of the Eye — Persistence of Vision — Subjective Colour Phenomena 
— Colour Blindness Pages 91-104 

CHAPTER V. 
CONTRAST. 

Contrast — Simultaneous Contrast — Successive Contrast — Contrast of Tone — 
Contrast of Colours — Modification of Colours by Contrast — Colour Con- 
trast in Decorative Design Pages 105-122 



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VI CiONl'ENT'S. 

CHAPTER VI. 
COLOUR IN DECORATION AND DESIGN. 

Colour Harmonies — Colour Equivalents — Illumination and Colour — Colour 
and Textile Fabrics — Surface Structure and Colour . . Pages 123-146. 

CHAPTER VII. 
MEASUREMENT OF COLOUR. 

Colour Patch Method — Colorimeters — The Tintometer — "^ 

Chronometer Pages 147-166 

Index Pages 157-160 



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LIST OF COLOURED PLATES. 

I. Absorption Spectra op Dyes Frmitispiece 

II. Effect of Mixing Colours Facing page 16 

III. Absorption Spectra and Effect of Mixing 

Coloured Lights „ 32 

IV. Effect of Mixing Colours ,, 48 

V. Colour Contrasts ,, 64 

VI. Colour Contrasts ,, 80 

Vn. Illustrating Three-Golour Process of Printing ,, 88' 

VIII. Colour Contrasts * ,, 96 

IX. Colour Contrasts „ 112 

X. Colour Contrasts ,, 128 

XI. CoiiOUR Contrasts ..,,,,. „ 144 



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COLOUR. 

CHAPTER I. 
COLOUR AND ITS PRODUCTION. 

Light. — Some objects, such as the sun, a gas flame, a 
candle flame, an electric lamp, etc., emit their own light ; these 
_are known as self-luminous bodies, we see them by reason of 
the light they emit. Other objects, comprising the great 
majority of those known to us, do not emit light, and there- 
fore are non-luminous. Such objects are rendered visible by 
reflecting the light which falls upon them from a luminous 
source. This fact is demonstrated every day when, upon the 
sun going down, objects become invisible ; similarly in tunnels, 
where absolute darkness reigns, non-luminous objects which 
pass in lose their visibility. 

Colour. — Not only is light necessary for the perception of 

a non-luminous object but it is also to the light which falls upon 

them that bodies owe their colour. Go into a flower-garden 

at mid-day, when the flowers will show many and variegated 

tints, from the faintest tint on the blush rose to the darkest 

and most deeply coloured dahlia — pinks, reds, yellows, violets 

and blues, together with the variegated shades of green of the 

foliage. Go into the same garden at night : all the colours then 

will have vanished, the foliage and flowers alike appearing of a 

neutral tint. Colour, therefore, is the product of light. The 

same inference may be drawn in the different appearance of a 

room at night, before and after the light is extinguished. 

1 



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2 ^ . .• ..THE THEORY OF COLOUE. 

Dispersion of White Light. — How does light affect the 
production of colour ? The answer is to be found by studying 
the classical experiments of Sir Isaac Newton. Let the shutters 
of a window be tightly closed at mid-day, so that no light 
can enter. Make a hole in the shutter ; the light streaming 
in will pass across the room and appear as a bright spbt on 
the opposite wall. The path of the light will usually bb 
rendered visible as a beam or ray by its reflection from the 
dust particles which are then noticed to be floating in the air. 
If now a triangular glass prism is placed in the path of the 
sunbeam, in such a position that the ray passes through one 
edge of it, a change both in direction and character of the ray 
will be noticed ; instead of continuing in a straight line, it 
will be bent out of its course considerably, and will appear, at 
a greater or less distance laterally from its former position, 
not as a bright spot of white light, but as a band of variously 
coloured lights of the same character and position as the colours 
in the rainbow, which, as a matter of fact, owes its existence 
to a similar action. This band of coloured light is called the 
spectruniy the colours being known as spectral or apectruTn 
colours. 

This dispersion of white light by its passage through a 
prism is illustrated in Fig. 1, which represents the path of 
white light through one edge of a triangular prism A, the 
form commonly used in carrying out such experiments, al- 
though any other form will give similar results. The lines aa 
represent a ray of white light ; if no prism intervened the ray 
would strike the screen S at 6 ; but the ray of light passing 
into the prism at c is refracted in the direction cd ; and while 
passing out at d it is again refracted, proceeding in the direc- 
tion df; the light is now rendered divergent and therefore 
forms a band, ef, on the screen, S, not of white light, but of 
various colours, as shown in Plate 1. For convenient refer- 
ence Sir Isaac Newton divided the spectrum into seven parts 



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COLOUR AND ITS PRODUCTION. 



— red, orange, yellow, green, blue, indigo and violet — these 
being popularly spoken of as the seven colours of the spectrum 




Pig. 1. 

or rainbow; but it will be seen hereafter that this division 
into seven colours is a purely arbitrary one. The spectrum 
of white light is shown on Plate I, No. 1. 

METHODS OF PRODUCING THE SPECTRUM. 

There are several methods of producing colour from white 
light:— 

(1) By means of a glass prism ; 

(2) By means of a diffraction grating ; 

(3) By means of the polariscope ; 

(4) By means of phosphorescent and fluorescent bodies ; 

(5) By means of thin films ; 

(6) By the action of coloured bodies. 

I. BY MEANS OF A GLASS PRISM. Names of Colours.— 

When, as above stated, a beam of white light is passed 

through a prism, as shown in Fig. 1, it is dispersed, a band of 

coloured hght or spectrum being produced, Plate I, having at 



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4 



THE THEOEY OF COLOUR. 



one extremity red, and at the other violet. Newton, who 
first discovered this property of the prism, divided the spec- 
trum into seven divisions, viz,, red, orange, yellow, green, blue, 
indigo and violet. In enumerating the colours it is much 
better, however, to follow the nomenclature of Rood, and 
designate the principal colours as red, orange-red, orange, 
orange-yellow, yellow, green, cyan blue, blue and violet. No 
sharp line of demarcation, however, exists between these colour 
divisions, the red passing imperceptibly into the orange-red, the 
orange-red into the orange ; this into the yellow, the yellow 
imperceptibly into the green ; this into the blue and the latter 
into the violet ; so that in reality there are not simply seven 
colours in the spectrum, but an infinite number of colours, 
for many of which language fails to find sufficient names. 

Fixed Lines of the Spectrum. — Fraunhofer was the first to 
notice that the spectrum of sunlight was not entirely con- 
tinuous, but was intersected by a number of fine lines; Dr. 
WoUaston also made the same discovery. These lines, which 
are called the fioi^d lines, have an interest, since they form 
standards by means of which the various portions of the 
spectrum may be located — some of them, being much more 
prominent than others, are referred to by reference letters, 
commencing from the red end of the spectrum; these are 
shown in Fig. 2, which is due to Rood, who gives the following 
measurements of the various portions of the spectrum, on the 
assumption that the distance from A to H is divided into 1000 
parts. 

Fixed Lines of the Solar Spectrum. — The fixed lines of 
the spectrum sliown in the figure fall at the following 
places : — -^ 



A 





E 


. 363-11 


a 


. . . 40-05 


b 


. 389-85 


B . 


. 74-02 


F 


. 493-22 


C 


. 112-71 


G 


. 753-68 


D 


. 220-31 


H 


. 1000 



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COLOUR AND ITS PRODUCTION. 5 

Coloured Spaces of the Prismatic Spectrum. — The follow- 
ing table shows the positions occupied by the various colours 



H 



'Red. 



Orange-red. 
, Orange. 
Orange-yellow. 
Yellow. 

, Greenish-yellow. 
Yellowish-green. 



^ Green. 



. Cyan blue. 



Blue. 



► Violet. 



Fig. 2. 



as measured by Rood, which correspond closely with obser- 
vations made by the author : — 



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6 THE THEORY OF COLOUR. 

Extends from 
Red to 149 

.Orange-red . . ' 149 „ 194 

Orange »194 „ 210 

Orange-yellow 210 „ 280 

Yellow 230 „ 240 

Greenish-yellow. .:.... 240 „ 844 

Green 344 „ 447 

Cyan blue • . . 447 „ 496 

Blue 496 „ 806 

Violet 806 „ 1000 

Relative Space of the Spectrum Colours. — From these 

measurements the following table has been constructed, which 

shows the space occupied by each division or colour : — 

Red 149 

Orange-red 46' 

Orange 16 

Orange-yellow * . . .20 

Yellow 10 

Greenish-yellow and yellowish-green .... 104 

Green and blue -green .'108 

Cyan blue 48 

Blue and blue-violet 811 

Violet 194 

The two foregoing tables, however, do not give the full 
length of the spectrum, as in front of A there is a dark-red 
portion which gradually shades off into blackness ; while at 
the other end beyond H there is a faint greyish kind of tint 
which has been called lavender. It may be added that in 
making such observations it is necessary that each portion of 
the spectrum be screened from the rest, a matter which is 
very easily done, so that the effect of contrast (see Chapter 
III.) on the hues may be eliminated, and, further, it is desirable 
that the source of light be as bright as possible. 

The order of the colours in the spectrum is that of the 
wave lengths as shown below. It might be assumed that in a 
normal spectrum the position of each colour would be in pro- 
portion to the wave length, but we find that in the spectrum 
produced by a glass prism such is not the case ; thus in some 



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COLOUR AND ITS PRODUCTION. 7 

portions there is undue crowding, while in others the space 
occupied by the colours is unduly extended; this' is the case 
with the blue and violet end, notably the latter ; while the red, 
orange and yellow, particularly the orange and yellow, are 
much shortened. 

Wave Motion of Light. — Several theories have been de- 
vised to explain all the phenomena of light — that known as 
the undulatory theory being the one which the majority of 
physicists have hitherto accepted as most in accordance with 
the facts. This presupposes that all space, including the bodies 
in it, are permeated by an exceedingly light or even intangible 
form of matter known as the ether, and that light is propa- 
gated through this medium by means of vibrations or undula- 
tions or waves, just as waves in water are propagated and as 
sound waves in air are formed. In all cases of wave motion 
there is, practically, no transference of matter, etc., from the 
source of the movement onwards, but simply an undulation, 
which is imparted from particle to particle of the medium in 
.which the wave motion is travelling ; in this way effects are 
transmitted to considerable distances from the exciting cause. 
The sun, or other source of light, generates these vibratory 
movements in the ether, which ultimately reach the retina of 
the eye and give rise to the sensation of light. 

In waves we recogAise two factors — wave length and 
amplitude. On the surface of a liquid such as water in 
motion, the distance between the crests of two waves is known 
as the wave length ; while the height from crest to trough is 
known as the amplitude of the wave. It has been demon- 
strated that it is on the magnitude of the latter factor that the 
intensity, or the power of doing work, of the wave depends ; 
thus of two waves of the same wave length that which exhibits 
the greatest amplitude being the most powerful, this value 
varying as the square of the amplitude. 

In light, differences of wave length give rise to difference 



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8 



THE THEORY OF COLOUR. 



in colour ; thus the waves of red light are longer than those 
of violet light, while orange, yellow, green and blue light rays 
are intermediate in their wave lengths. 

The Fraunhofer lines, being fixed and therefore constant in 
position, have been utilised as standards for the measurement 
of the spectrum. They have been lettered, for ease of re- 
ference, from A in the red end of the spectrum to H in the 
violet end, the wave lengths of the light at these positions 
in the spectrum have been measured, the measurements being 

in tlie following table in units of ^oo ^ 
metre. 



Aj-i u.jC i.yji 


iv^wiiag vcbkji^ 111 u.uxi;o * 


ji Y 


0000000 ^*^ " "^' 




Wave lengths in 




ten-millionths 


Line. 


Position in spectrum. of a millimetre. 


A 


Red 7694 


B 


Red 






6867 


c 


Red-orange 






6562 


D 


Orange-yellow 






6892 


E 


Green 






5269 ' 


F 


. Blue 






4861 


G 


Violet 






4307 


H 


. Violet . 






3968 



II. BY MEANS OF A DIFFRACTION GRATING.— The 

second of the methods referred to above for decomposing 
white light — that of a diffraction grating — allows of a spec- 
trum of normal length in proportion to the wave lengths of the 
colours to be obtained. If the glass prism be replaced by a 
metal or glass plate ruled with a large number of fine hnes, in 
some cases 20,000 to the inch, and the light be reflected from 
its surface, a spectrum is obtained which contains the various 
colours almost but not quite in their true position ; this diffrac- 
tion spectrum is, however, much less intense than a prismatic 
spectrum. 

Fixed Lines of the Normal Spectrum. — Measurements made 
by Rood of a normal spectrum produced in this way give the 
position of the fixed lines as follows : — 



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Plate II. 




(Theory op Colour). Effect of Mixing Colours. To face p, i6. 



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COLOITE AND ITS PEODUCTION. 



A 





E . 


. 638-92 


a 


113-74 


b . 


. 664-79 


B 


201-61 


F . 


. 749-24 


C 


285-05 


G . 


. 902-07 


D 


468-38 


H . 


. 1000 



Positions of Colours in Normal Spectrum. — The next table 
gives the positions of the colours in the normal spectrum ac- 
•cording'to Rood : — 

Extends from 

Red to 330 

Orange-red 330 „ 434 

Orange 434 „ 469 

Orange-yellow 459 „ 485 

Yellow 486 „ 498 

Greenish-yellow 498 „ 695 

Full green . 695 „ 682 

Blue-green 682 „ 698 

Cyan blue 698 „ 823 

Violet-blue 823 „ 940 

Violet 940 „ 1000 

Spaces Occupied by the Colours in a Normal Spectrum. — 
The amount of space occupied by each colour in such a spec- 
trum is shown in the following table : — 



Pure red 

Orange-red . . . . 

Orange 

Orange-yellow .... 

Yellow 

Greenish-yellow and yellow-green 

Full green 

Blue-green . . 

Cyan blue 

Blue 

Violet-blue and blue-violet 
Pure violet 



330 
104 
25 
26 
13 
97 
87 
16 
61 
74 
117 
60 



If white light can be subdivided into these coloured lights, 
the question arises whether the spectrum colours themselves 
may not be further affected by passage through a second 
prism, ai^ shown in Fig. 3. Here A represents a beam of 
white light which is caused to pass through a prism P, hence 



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10 



THE THEOEY OF COLOUE. 



becoming dispersed, the rays falling on the sqreen B, an. 
opening in whitjh permits of a portion C passing through and 
entering a second prism D where it undergoes further disper- 
sion, appearing ultimately on a second screen E at H. The 
twice dispersed rays, however, are not altered in kind from 
the rays which enter the second prism, but are simply widened 
out at H, Therefore each portion of the spectrum consists of 
only one kind of coloured light rays. 

Spectroscope. — An instrument by means of which white 
light can be resolved into its constituent colours, and by which 
other observations on colour can be made, is known as the 
spectroscope. An instrument of this kind is shown in Fig. 5, 




Fig. 3. 

In its simplest form it consists of three parts. First, a tube 
which carries at one end a slit arrangement by means of which 
a narrow beam of light can be projected into the tube, while 
at the other end is a lens, called a coUimating lens, for the 
purpose of converting the divergent rays which pass through 
the slit into parallel rays. Second, a glass prism, through 
which the rays from the slit are passed ; and, third, a telescope 
by means of which the spectrum thus produced may be ob- 
served. 

Fig. 4 is an illustration of Browning's direct vision spectro- 
scope, a useful form for taking observations of the absorption 
spectra of coloured glasses or coloured liquids, it being only 
needful to hold the glass or a cell containing the liquid 



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J 



COLOUK AND ITS PKODUCTION. 



11 



against the end of the apparatus, and direct the instrument 
to the sky, when the spectrum will be observed. 

In many instruments only one prism is used, but if a wider 
dispersion of the rays is required then more are added, spectro- 
scopes with six prisms having been made. In some instru- 
ments there is also an arrangement by means of which a 




Fig. 4. 
graduated scale can be projected into the field of view ojf the 
telescope, so that measurements of the spectrum can be made. In 
some instruments arrangements are made whereby two spectra 
can be brought side by side for the purpose of comparison. 
A diffraction spectroscope is similarly constructed, except 




Fig. 6. 

that the prism is replaced by a diffraction grating, the light 
passing through the slit and coUimating lens being reflected 
into the telescope from the grating (see page 6). 

Recomposition of White Light. — As white light can be 
subdivided into many coloured lights, it is possible by re- 
combining these coloured lights together to reproduce white 



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12 



THE THEORY OF COLOUR. 



light ; this can be effected in several ways. One method shown 
in Fig. 6, in which the dispersed beam produced by the prism 
A is received upon a concave mirror B from which it is re- 
flected to a point D, where the various coloured rays are all 
converged to again form white light; Instead of using a single 




WHITE 



Fig. 6. 



concave mirror, the various portions of the spectrum produced 
by the prism may be received on a series of mirrors each being 
reflected to one spot where white light will be re-formed. 

Another plan, the principle underlying which has been 
found very useful in the construction of lenses for microscopes 




Fig. 7. . 
and other optical instruments, is to pass the rays from the 
dispersing prism through a second one placed in the reverse 
position, as shown in Fig. 7, where the path of the rays of 
light through the two prisms is traced. It may be pointed 
out in passing that the degree of dispersion varies with dif- 



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COLOUR AND ITS PRODUCTION. 13 

f erent kinds of glass — a prism made of flint glass, being more 
dense and refractive, disperses the light much more than a 
similar prism made of crown glass. The passage of light 
through lenses is always accompanied by a certain amount of 
dispersion, which interferes with the definition of objects, 
surrounding them with a fringe of coloured light, which 
phenomenon is known as " chromatic aberration ". This can 
be remedied by making the lens a compound one, a convex 
lens of crown glass being combined with a meniscus or plano- 
concave lens of flint glass, the latter by its greater dispersive 
power neutralising the chromatic aberration of the crown glass 
lens, while the compound lens acts like a simple convex lens 
to the light rays which pass through it. 

Another, but not so perfect a method of combining colours 
is to paint a white card disc in radial divisions with the seven 
principal colours of the spectrum, as at 1 in Plate II. If this 
be made to rotate by means of the mechanism shown in Fig. 
44, then, by the operation of persistence of vision, which will 
be more fully dealt with in another chapter, the various 
colours appear to blend into one another, and a neutral tint or 
greyish- white appears. A pure white can never be obtained 
by this method, by reason of the fact that the pigments used 
in painting the disc are never pure in colour, a point which will 
be noticed later. 

Hue, — There are three constants, as they are called, which 
belong to every colour ; these are hue, luminosity and purity. 
The kTJue of a colour is that constant which is commonly de- 
nominated by the term colour, as blue, green, red, yellow, rose, 
or violet, all which terms are employed to distinguish the 
particular colour sensations one from another. The only true 
standards for hue are the spectrum colours, and we may 
measure the hue of any particular colour by noting the posi- 
tion in the spectrum which it occupies or by determining the 
wave length of the rays coming from it. The following table 



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14 



THE THEOKY OF COLOUK. 



gives the position in the normal spectrum, together with the 
<3orresponding wave lengths of the light reflected from discs 
painted with various pigments in imitation of the spectrum 
•colours : — 











Wave length in 


Position in the * ten-millionths of 


fame of the colour. normal spectrum. 


a millimetre. 


Vermilion 


387 . 


6290 


Bed lead 






422 . 


2061 


Chrome yellow 






488 . 


5820 


Emerald green 






648 . 


5284 


Prussian blue . 






740 . 


4899 


Cobalt blue . 






770 . 


4790 


Ultramarine (natural) 






785 . 


4785 


Ultramarine (artificial) 






867 . 


4472 


Same tinted with Hoffm 


an's ^ 


Violet BB. 


916 . 


4267 



Very minute differences in tlie hue of colours, although dis- 
tinguishable by the eye, are almost beyond description by any 
form of notation. Aubert, many years ago, made experiments 
on the sensitiveness of the eye to changes of colour by means 
of coloured discs. It was thus found that the addition of one 
part of white light to 360 parts of coloured light induced a 
<;hange which was clearly perceptible, changes amounting to 
<^iily TTO ^o ^^ part of colour being readily perceived. Aubert 
states that more than a thousand hues are distinguishable in 
the spectrum, and it is possible to recognise even small varia- 
tions of these hues. The addition of one part of Chinese blue 
to 400 parts of barytes is suflScient to impart a very perceptible 
blue tint to the latter, while the addition of an equal quantity 
of chrome yellow to such a mixture causes a change in hue, 
making it become more greenish. Mr. Charles Pierce has also 
made experiments on this subject, and has found that the 
perceptive faculty of the eye is the same for all the spectrum 
-colours. 

Luminosity. — The second constant of light is luminosity or 
brightness. A sheet of yellow paper appears to the eye to be 
much brighter or more luminous than a sheet of red paper, or 



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COLOUE AND ITS PBODUCTION. 



15 



a sheet of blue paper. Given equal illumination, the most 
luminous surface is a white one; the least luminous, a black 
one ; and between these two there are degrees of luminosity. 
It is possible to measure the relative luminosity of the spectrum 
colours by isolating each one and ascertaining relatively the 
amount of white light which is equal to it in luminosity. 
Working in this manner the following scale of luminosity has 
been obtained, the spectrum being divided into 1000 parts be- 
tween the fixed lines A and H as in the tables which have 
previously been given : — 

LUMINOSITY OF THE SPECTRUM COLOURS. 



Colour. 


Position in spectrum. 


Luminosity. 


Dark red . 


Frorf 40-5 to 67 


80 


Pure red . 


„ 


104-6 „ 112-7 . 


493 


Red . 


a 


112-7 „ 138 . 


1100 


Orange-red 


»f 


158-5 „ 168-5 . 


2773 


Orange and orange-yellow 


>» 


189 „ 220-3 . 


6985 


Orange-yellow . 


>» 


220-3,, 281-6 . 


7891 


Greenish-yellow to green 


»> 


231-5 „ 363 


3033 


Blue-green and cyan blue 


)i 


390 „ 493 


1100 


Blue .... 


It 


623-6 „ 689-6 . 


493 


Ultramarine 


>» 


498 „ 568-6 . 


90-6 


Blue violet 


»i 


763-5 „ 825-6 . 


36 


Violet 


»» 


896 „ 956 


13 



The relative luminosity of the spectrum colours is also shown 
graphically in Fig. 8, where the vertical lines indicate the 
position of the spectrum colour and the horizontal lines the 
luminosity. It will be seen that the most luminous portion of 
the spectrum is the yellow and orange, while the luminosity 
declines very rapidly on either side to the red or violet. It 
may be mentioned that the luminosity of the colours as viewed 
by persons who may be colour blind will differ from the lumin- 
osity as seen by a person of normal sight. This subject will 
be subsequently referred to. 

Another method of determining the luminosity of colours is 
by the employment of the apparatus shown in Fig. 44, which 



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16 



THE THEOEY OF COLOUE. 



will be more fully described in Chapter III. A large disc 

of card coloured with a pig- 
ment, the luminosity of the 
colour of which is to be de- 
termined, is placed on the 
spindle of the revolving ap- 
paratus ; on this spindle are 
also fixed two overlapping 
discs of black and white 
paper, these being so arranged 
(see Chapter III.) that the 
relative proportions of black 
and white exposed can be 
varied. When all is ready 
the combined discs (which 
have, when at rest, the ap- 
pearance shown in Fig. 47) 
are revolved; the black and 
white then amalgamate and 
give the sensation of grey, 
which is more or less lumin-. 
ous according to the propor- 
tions of white and black ex- 
posed ; by varying the pro- 
portions a grey is obtained 
which will appear to have 
the same intensity as the 
colour whose luminosity is to 
be measured. Then, assum- 
ing that white light has a 
luminosity of 100, the lumin- 
osity of the colour will be 
that of the quantity of white 
exposed in the black and 
white discs. A small error 



1 I 1 1 1 1 I . 1 1 11^ 


i 






i t 


t 


t 


t^ 


y 


• t :? 


/ 


t ' 


/ 


/ 


^^ "s 


7^ -8 
^ 


^^ 


>^ 


/ 


, s 


I 


"^^ ? 


^v. 


"^ 


^ § 


> ^ 


X ' 


4 


-\ 


\ ? 


t^ 


i 






% 


■ffS 






. 


4-t 



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COLOUE AND ITS PEODUCTION. • 17 

is introduced if the assumption is made that the black disc 
has no luminosity, since it has a small luminosity, usually 
about 4 to 5 per cent, of that of a white disc. The author 
has obtained the following results by this method : — 

White paper 100 

Vermilion 20'6 

Orange-red 40*3 

Ochre ........ 56'6 

Chrome-yellow ...... 61*1 

Emerald green 51*4 

Green 50 

Ultramarine 50 

.Blue 20-6 

Umber 22-2 

These measurements are not easy to make, but by taking 
the mean of several sets of observations a fair approximation 
to the truth may be obtained. 

Compared together it is possible for two colours, a red and 
a blue for example, to appear of the same degree of lumin- 
osity. 

Extent of surface has some effect in influencing impres- 
sions of luminosity. A large surface of colour of low lumin- 
osity will appear to overpower a small surface of colour of 
high intensity, the two colours appearing to have the same 
luminosity. Artists are well aware of this fact, and often 
take advantage of it in painting, introducing a spot or patch 
of a fiighly luminous colour into a mass of dark, sombre 
colouring with very good effect. 

The judgment of equal luminosity of different colours is, 
perhaps, a psychological one, two observers may not regard 
the same pair of colours as equally luminous, just as in 
different persons the perception of shade and tint in colours 
varies so that in matching colour tints no two people will 
arrive at precisely the same results. 

Purity. — The third constant of colour is purity. By 
purity of colour is meant the absence from a colour of any 

2 



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18 



THE THEORY OF COLOUR. 



admixture of another colour or of white light. The standard 
of purity in all cases is the spectrum, the spectral colours 
being absolutely pure ; they are, therefore, the standard for 
comparison with the light which comes from coloured objects, 
painted surfaces, etc. When the comparison is made it will be 
noticed that while such surfaces or coloured bodies may- 
correspond in hue with some portion of the spectrum, yet 
the coloured surface appears pale in comparison with the 
spectrum colour; this is due to the colour which is being 
compared being diluted with more or less white light. If, 
however, we make a mixture of the spectral colour with 




Fig. 9. 

white light it will be possible to reduce the intensity of the 
spectral colour to that of the coloured surface ; then if the 
amount of white light added be measured, it necessarily gives 
the amount of white light admixed with the colour in 
question. Fig. 9 shows one method of mixing white light 
with the spectral colours. 

In this drawing ABC represents a glass prism, S is a 
beam of white light passing through a hole, F, in a shutter, 
EG; this light, after passing through the prism, forms a 
spectrum, P, on a screen, MN ; another beam of white 
light from S passing through another hole in the shutter, 
EF, falls upon a mirror, L, and is reflected thence to the 



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COLOUR AND ITS PRODUCTION. 19 

screen at O ; by tilting the mirror, L, the white light may 
be thrown upon any part of the spectrum, P, and its effect 
upon the different colours observed. 

Thus, for instance, vermilion, or rather the light reflected 
from a surface painted with this pigment, can be matched 
by mixing the light from a portion of the red end of the 
spectrum with 20 per cent, of white light. In a similar way 
it has been ascertained that emerald green reflects nearly 
the same amount of white light, and ultramarine about 25 
per cent. The effect of white light when mixed with the 
coloured light is to reduce its intensity, and thus soften it, 
causing it to have less action on the eye ; when the proportion 
of white light is considerable the influence of the coloured 
light is reduced to such an extent that it becomes almost 
invisible, and we then get what are termed grey tints vary- 
ing in tone — reddish, greenish, bluish, etc.^ — according to the 
colour from which they are produced. This question will be 
discussed in detail in another chapter. 

III. PRODUCTION OF COLOUR BY THE POLARISCOPE.— 

When a ray of white light is passed through a prism of Ice- 
land spar, i,e. a transparent crystal of calc spar, it undergoes 
what is known as double refraction ^ that is one portion of 
the ray is refracted more than the other, so that we get two 




Fig. 10. 

rays which pass out of the prism parallel to one another (see 
Fig. 10). These two rays possess properties different from 
the original ray of white light; they have become what is 
rather inaptly termed polarised. If the prism of Iceland 
spar be cut in two diagonally and the two surfaces cemented 



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20 THE THEORY OF COLOUR^ 

together, then it is found that while one ray passes through 
the division unchanged, the other ray is reflected from the 
cemented surface and passes out at the side of the prism. A 
prism thus cut and arranged, known as a NicoVs prism, forms 
a very convenient means of obtaining polarised light for 
experimental purposes ; its effect on a ray of light is shown in 
Fig. 11. 

The NicoFs prism is shown with the diagonal cut AB, the 
two halves being cemented together with Canada balsam. 
A beam of light, C, entering the prism at D, becomes doubly 
refracted during its passage through the prism ; on reaching 
the cemented surface AB, one of the two beams is reflected to 
the side of the prism, as shown in the drawing, while the 
other passes through the prism unaltered. 




Another manner of obtaining polarised light is by reflection 
from a bundle of glass plates (see Fig. 13). It has been 
found that, when a plate of glass is placed at an angle of 33*" 
to the incident ray, the light which is reflected is very largely 
polarised ; by emplo3ring a bundle of glass plates the effect is 
increased and a sufficient quantity of polarised light obtained 
to perform a large number of experiments. If the light from 
such a bundle of plates is caused to pass into a Nicol's prism 
it is found on rotating the latter that in one position of the 
prism the light passes through unchanged, while at a right 
angle, i.e. 90°, to this no light whatever emerges. The 
same effect can be produced if a second bundle of glass plates 
is employed; if this second bundle is arranged with their 
faces towards the polarising bundle then the light is re- 
flected ; on the other hand, if they have their edges towards 



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COLOUE AND ITS PEODUCTION. 



21 



the polarising bundle the light is not reflected but passes 
through the second bundle of plates. If a piece of selenite 
be interposed between the two bundles of glass plates its 
reflection on the second bundle will be more or less coloured, 
and on rotating the second bundle of plates it will be found 
that the colour changes according to the position of the 
bundle. If instead of the selenite a piece of rock crystal cut 
perpendicular to the axis of the crystal be interposed, colour 
will also be produced, this colour also changing as the second 
bundle of plates is rotated. 

The instrument employed to produce polarised light is 




known as the polariscope, A simple form of this instru- 
ment is shown in Fig. 12 ; while Fig. 13 is a diagrammatic 
representation of it. A bundle of glass plates, A, rests on 
the bottom of the box, this represents the polariser ; light at 
the requisite angle is allowed to fall on this bundle of glass 
plates, -and being reflected upwards is received in the analyser, 
B, which may either be a NicoFs prism, as in the instrument 
illustrated, or a bundle of glass plates. The objects, if large, are 
placed on the support D ; or, if small, are held in a support E, 
while at F is a lens for focussing the light on the objects when 
these are placed at E, or when these are placed at D, on the 



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22 



THE THEORY OP COLOUR. 



analyser B. C is a ground glass plate which diffuses the light 
falling on the plates A, Polariscopes are now fitted to most 
microscopes, both polariser and analyser containing a Nicol's 




Fig. 13. 



prism, the former being placed under the stage of the micro- 
scope, while the latter is fitted directly above the objective 
or over the eye-piece. 

Another form of the polariscope is shown in Fig 14. In 




Fig. 14. 



this drawing, A is a bundle of glass plates, the polariser, 
while the enclosing tubes CD are so arranged that the light 
strikes the plates at the proper angle (see above) ; B is a 
similar bundle of glass plates, the analyser, in which the 



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COLOUE AND ITS PEODUCTION. 23 

effects produced by the passage of the polarised light from 
A can be observed. This drawing shows a form of polariscope 
suitable to be used either as a table polariscope for individual 
observation or as a polariscope in conjunction with the optical 
lantern for demonstrations to a number of persons. 

Many substances, when placed between the polariser 
and analyser, give rise to the production of chromatic effects ; 
thin plates of selenite, in particular, being useful for this 
purpose. The colour produced is dependent upon the thick- 
ness of the plate — thus one particular thickness will give 
rise to a yellow colour, another to a red, another to a green — 
if the plate of selenite is of uneven thickness then quite a play 
of colours will be produced. On rotating the analyser the 
colours change, and when the analyser has been rotated 
through a quarter of a revolution the colour produced is 
complementary (see Chapter III,) to that originally obtained. 
If a quartz plate be used, then, as the analyser is rotated, 
the colours follow each other in the order of the spectrum — 
changing from red to orange, orange to yellow, yellow to 
green, and so on. Some quartz crystals require the analyser, 
to be rotated to the right in order to obtain the colours in 
this order — such are known as right-handed (dextro-rotatory) 
crystals ; others require the analyser to be rotated to the 
left — such being known as left-handed (laevo-rotatory) crystals. 
Some solid bodies, although not producing any chromatic 
effect, have an action on the ray of polarised light. It has 
been stated above that when the analyser is at right angles to 
the polariser no light is transmitted ; if now a substance of 
this class be introduced between the polariser and the analyser, 
light will again be transmitted, but without colour — this 
shows that the interposed substance has some action on the 
ray which passes through it On rotating the analyser 
through a small angle the light is again obliterated, showing 
that the substance has a rotatory action on the ray of polarised 



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24 THE THEORY OF COLOUR. 

light: some require the analyser to be rotated to the right, 
these fitre called dextro-rotatory bodies ; while others require 
it to be rotated to the left, these are called lasvo-rotatory 
bodies ; this action is strictly quantitative and by means of it 
many substances, as sugar, turpentine, etc., can be estimated, 
this property is, therefore, of value from an analytical point 
of view and is often taken advantage of. This feature of the 
subject is, however, beyond the scope of the present work. 

When the ray of polarised light is caused to pass along 
the optic axis of certain crystals — potassium nitrate, tartaric 
acid, borax, calcite, sugar, iferrocyanide of potassium, phos- 
phate of potassium, etc. — the analyser exhibits a very fine 
effect; this consists of a series of concentric coloured circles 
round the axis of the crystal, and lying upon these is a black 
cross; on rotating the analyser, the black cross gives place 
to a white one, while the concentric rings change colour 
and assume the complementary hues; the brilliance of the 
colours being great. The character of these phenomena vary 
with different substances : in some cases the rings are sharply 
defined ; in others, they pass insensibly into one another ; .in 
some the black cross is prominent, while in others it is but 
faint. Some crystals are biaxial, and, therefore, two sets of 
coloured rings and two black crosses, more or less intersecting 
one another, are obtained. 

When masses of crystals which act on polarised light are 
allowed to form in thin layers on a piece of glass, these 
crystals, viewed in the polariscope, give rise to such beautiful 
colour effects that they almost defy description; once seen, 
however, they are not readily forgotten, on account of the 
harmony of colouring which prevails; the immense variety of 
form and of colour which is presented by different substances 
is nevertheless marvellous. 

Glass which has been heated and then suddenly cooled, 
or has been subjected to a strain, also produces colour effects ; 



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COLOUR AND ITS PRODUCTION. 25 

in this case the concentric coloured rings and black cross some- 
times appear ; at others, various effects, according to the con- 
-ditions. 

Starch grains when viewed under a microscope fitted with 
^ polariscope show black crosses in a similar way to crystals, 
in some cases the appearance is characteristic and suffices to 
•distinguish a particular starch from others. 

It is quite beyond the scope of this book to enter into a 
full account of the phenomena of polarised light or attempt 
An explanation of how and 
why these effects are pro- 
educed; the reader is referred 
to books dealing specially 
with this subject for such in- 
formation. There is, however, 
just one other point that may 
be touched upon, seeing that ^^^* ^^* 

it has a bearing upon the production of colour. 

If, instead of using a NicoFs prism as an analyser, a 
«imple prism of calcite be substituted, the light from the 
polariser being allowed to fall on this prism through a small 
diaphragm, then, on looking through the eye-piece of the 
instrument, two white discs will be observed overlapping (as 
shown in Fig. 15). If, now, between the polariser and the 
calcite prism be placed a thin plate of selenite, the discs will 
-appear coloured, the colours varying, with the thickness of the 
£lm of selenite ; the chief feature, however, about them is that 
the two discs appear of different colours, these being comple- 
imentary to one another — thus, while one may be green the 
other will be red, one yellow and the other blue, and so on. 
Where, however, the discs overlap one another this portion 
is usually white, showing that by the union of two comple- 
anentary colours white light may be formed, see Plate III., 
No. 5 et seq. This has a very important bearing on the 



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26 THE THEORY OF COLOUR. 

theory of colour,^which will be developed in a subsequent 
chapter, 

IV. COLOUR PRODUCED BY PHOSPHORESCENCE AND" 
FLUORESCENCE. — Certain compounds, notably the sulphides 
of barium, strontium and calcium, in the state of a fine powder 
when exposed to bright light, and then taken into a dark 
room, are found to glow with light, differing in hue or tint 
in each case; such glow is known as phosphorescent light. 
The nature or cause of this phenomenon is not thoroughly^ 
understood, but research has shown that a large number of 
bodies are capable of exhibiting phosphorescence when first 
exposed to a bright light, as from burning magnesium, and 
then viewed in a dark place. Some substances exhibit this- 
phenomenon more strongly under a vacuum than they do- 
under ordinary conditions. The production of the so-called 
" luminous paint,*' which shines in the dark after exposure to- 
light, is based on this property of barium and strontium sul- 
phides being used. 

When a solution of eosine in alcohol is viewed by trans- 
mitted light it appears of a pale crimson colour, yet wheni 
looked at direct it exhibits a beautiful yellow glow, which is 
known as fluorescence. Many substances are found to have^ 
this property, and are termed dichroic. Glass tinted or 
coloured with uranium has this property; when looked 
through it shows a pale yellow tint, yet it reflects a bluish- 
green light. Uranium glass has another property*: if placed 
in a dark room and illuminated with violet light it does not 
reflect violet light, but appears to glow or to be self-luminous,, 
the light having a bluish-green tint; this change of hue is 
very remarkable, because it would appear as though the 
uranium glass had the property of changing the wave length: 
of the light which falls upon it. A change in colour can only 
be accounted for by a change in the wave length of the emitted 



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COLOUR AND ITS PRODUCTION. 27 

light. Stokes has made numerous experiments on uranium 
glass and substances which act on light in a similar manner ;^ 
he finds that in each case the wave length is affected and, 
further, that the alteration consists in an increase. The pro- 
perty of fluorescence is possessed by many substances, e.g.^ 
platino-cyanide of barium, thallene, etc., etc, 

V. PRODUCTION OF COLOUR BY INTERFERENCE.— 

When an oily substance is dropped upon the surface of water 
it spreads over the latter in the form of a very thin layer, 
giving rise to the production of a play of beautiful colours 
which, chameleon-like, rapidly changes in hue and extent. 
These colours are produced in a peculiar manner ; the waves^ 
of light impinging upon the film of oil undergo both refraction 
and reflection, the film, however, is so thin that the waves of 
light reflected from its upper and lower surfaces clash with 
one another, whereby some are quenched, the remainder pass- 
ing forward to the eye of the observer as coloured light ; the 
degree of quenching depends upon the thickness of the film,, 
and as this is constantly changing, the colours likewise vary. 
Interference colours are also produced when light is reflected 
from regularly marked surfaces where the markings are very 
minute. 

Interference colours are frequently met with in nature :: 
the exquisite colouring found on many beetles' wings, the, 
iridescent hues seen in many shells, the pearly tints of fish 
scales, the colours on many birds' feathers are due to this- 
cause. The colours on a soap bubble, the hues of many 
minerals, and the iridescence of many varieties of glass are 
due to interference. 

For the purpose of showing the colours of thin films the 
apparatus illustrated in Fig. 16 may be used. This consists 
of a plano-convex lens, CD, and a double-convex lens, AB, 
both of long focal length, and three pairs of screws, PP, for the- 



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■28 



THE THEORY OF COLOUR 



ipurpose of screwing them together and producing a regular 
j)ressure at the point where the two lenses touch each other. 
By pressing the lenses together there appears a black spot in 
4ihe centre with a series of coloured rings or spectra concen- 




FiG. 16. 



-tred round it as shown in Fig. 17, which represents about one- 
half of the system ; the farther each ring may be from the centre 
the fewer are the colours in it. This is the effect as seen by 
reflected light. If the rings be viewed by transmitted light. 







Fig. 17. 



then the central spot appears to be white, and the system of 
rings are seen in colours which are complementary to those 
observed by reflected light. Fig. 18 shows the order of the 
tints passing from the centre outwards as seen by reflected 



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OOLOUB AND ITS PRODUCTION. 



29» 



Reflected 
Tints. 

Red. 
Green. 

Red. 
Yellow. 
Green. 

Blue. 
Purple. 

Red. 

Yellow. 

Green. 

Blue. 

Violet. 

Red. 

Yellow. 

White. 

Blue. 

Black. 

Blue. 
White. 
Yellow. 

Red. 
Violet. 

Blue. 

Green. 




Transmitted 
Tints. 

Bluish green. 

Red. 

Bluish green. 

Violet. 

Red. 

Yellow. 

Green. 

Blue. 

Violet. 

Red. 

Yellow. 

White. 

Blue. 

Violet. 

Black. 

Yellowish-. 

White. 

Yellowish.. 

Black. 

Violet. 

Blue.. 
White. 

Yellow. 

Red. 



YeUow. 
Red. 


\ Violet. 
\ Blue. 


Purple. 

Blue. 

Green. 

Yellow. 


\ Cireen. 
\ Yellow. 

\ Red. 

\ Violet. 


Red. 

Green. 

Red. 


\ Bluish green 
\ Red. 
\ Bluish green 



Fig. 18. 



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30 



THE THEORY OF COLOUR. 



SIR ISAAC NEWTON'S TABLE OF THE COLOURS OF THIN PLATES 
OF AIR, WATER AND GLASS. 





Colours produced at the thicknesses 


Thickness in mil- 




stated in the last three columns. 


lionths of an inch. 


SuccesflioQ of Spectra, or 
Orders of Colours. 










Reflected. 


Transmitted. 


Air. 


Water. 


Glass. 




Very black. 




* 


8 


if 




Black. 


White. 


1 


1 


If 




Beginning of black. 




2 


14 


If 


First Spectrum, or 


Blue. 


Yellowish-red. 


n 


n 


1** 


order of colours. 


White. 


Black. 


H 


3J 


3» 




Yellow. 


Violet. 


H 


5il 


H 




Orange. 




8 


6 


H 




Red. 


Blue. 


9 


6} 


H 




Violet. 


White. 


IH 


3| 


n 




Indigo. 




m 


9| 


8f 




Blue. 


Yellow. 


u 


lOi 


9 


Second Spectrum, or 


Green. 


Red. 


15S 


11* 


9f 


order of colours. 


Yellow. 


Violet. 


16i^ 


12* 


10* 




Orange. 




17| 


18 


11* 




Bright red. 


Blue. 


18* 


ISf 


llj 




Scarlet. 




19^ 


141 


m 




Purple. 


Green. 


21 


15* 


13** 




Indigo. 




22,V 


17f 


14: ■ 


Third Spectrum, or 
order of colours. 


Blue. 

Green. 

Yellow. 


Yellow. 
Red. 


27i 


17H 

ISA 
20* 


ISiS 
ITJ 




Red. 


Bluish-green. 


29 


21f 


18? 




Bluish.red. 




32 


24 


m 




Bluish- green. 




24 


25} 


22 


Fourth Spectrum, or 
order of colours. 


Green. 


Red. 


36^ 


26i 


22| 


Yellowish-green, 




36 


27 


23f 




Red. 


Bluish-green. 


40} 


SOJ 


26 


Fifth Spectrum. 


Greenish-blue. 
Red. 


Red. 


46 
52} 


S4J 
39i 


39} 
34 


Sixth Spectrum. 


Greenish-blue. 
Red. 




58J 
65 


44 
481 


38 
42 


Seventh Spectrum; 


Greenish-blue. 
Reddish-white. 




71 
71 


68J 
67« 


m 
m 



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COLOUB AND ITfe PRODUCTION. 31 

^nd by transmitted light. It may be stated that a layer of 
air ceases to reflect light when the thickness is less than half 
a millionth of an inch ; that with a thickness of more than 
seventy-two millionths of an inch it reflects white light, and 
that between these two limits it reflects colours in various 
degrees. In the same way water of a thickness of three- 
eighths of a millionth of an inch ceases to reflect light ; above 
fifty-eight millionths of an inch it reflects white light, and 
other colours at intermediate thicknesses. Glass of a thick- 
ness of one-third of a millionth of an inch does not reflect 
light ; at a thickness of fifty millionths of an inch it will re- 
flect white light. Sir Isaac Newton, who investigated the 
colours of thin films, has given the table, on opposite page, 
of the various spectra which can be observed, together with 
the varying thicknesses of air, water and glass at which they 
are obtained. 

The production of colour when white light falls on 
<5oloured bodies, the sixth of the ways enumerated at Jbhe 
head of this chapter, is of sufficient importance to merit dis- 
cussion in a separate chapter. 



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CHAPTER II. 
CAUSE OP COLOUR IN COLOURED BODIES. 

VI. PRODUCTION OF COLOUR BY THE ACTION OF 
COLOURED BODIES. — We have now to discuss, as far as may- 
be possible, the reasons why any particular substance presents ' 
itself to our eyes as coloured. The final answer to this 
question cannot really be; given, as we are still unable to 
state definitely why one substance should have a red colour, 
another one blue, and still another one green. For a complete 
answer we shall have to learn more of the intramolecular 
stiuicture of bodies than we know at present in order to 
ascertain why they are able to select some of the rays of light 
and absorb them, while other rays are not affected ; possibly 
we may find that the molecules of these bodies are in such a 
state of motion as to enable them to submerge light rays of 
certain wave lengths while others remain unchanged. 

We see coloured bodies under two conditions : in the first 
the material being transparent the light comes to our eyes 
through the substance, or is transmitted, as is the case with 
stained glass, coloured solutions and liquids, etc.; while in 
the second case, more particularly with opaque bodies, the light 
is reflected from the object to our eyes. We will first consider 
colours produced by transmission and subsequently the colours 
due to reflection. 

Transmitted Colours. — When white light passes through 
coloured glass, and from thence to the eye of the observer 
appearing as coloured light, then, to produce such light, it is 

(32) 



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Plate III. 




(ThborV of Colour). -Absqrption Spectra and Effect of Mixing Coloured Lights. 

To face p, 32. 



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CAUSE OF COLOUR IN COLOURED BODIES. 33 

evident that the glass must have had some action on the light ; 

probably it has absorbed some of the rays which go to make 

up the white light that fell upon it and permitted others to 

pass through, the nature and degree of absorption depending 

upon the composition of the glass and the .character of whai 

we call the colouring matter present therein. 

To understand fully the nature of the absorption of light 

by coloured bodies we- must observe the spectrum of the rays 

which are transmitted, and compare these with the spectrum 

of white light. This is a comparatively simple matter : if the 

object to be examined is coloured glass then it suffices to 

hold it in front of the slit of an ordinary spectroscope ; or, 

in the case of a coloured solution or liquid, to hold a glass 

vessel containing it in front of the slit. With regard to dyes 

from coal tar their absorption spectra can very conveniently 

be obtained by a plan described by Mr. Arthur Dufton : an 

ordinary photographic dry plate is taken, and the silver salts 

removed by placing the plate in a bath of hyposulphite of 

soda and thoroughly washing afterwards ; the plate is next 

immersed in a weak solution of the dye stuff. In the case of 

the basic and direct dyes such as Magenta, Safranine, 

Chrysoidine, Chrysamine, Benzo blue, etc., no addition need 

be made to the solution ; but with acid and azo colours, such 

as Acid green, Naphthol yellow, Orange, Eosine, etc., a few 

drops of acetic acid may be added. Any depth of colour may 

be obtained on the plates within limits by regulating the 

duration of immersion in the dye solution ; in time, however, 

the gelatine film on the plate becomes saturated with the 

colour, and no further increase in intensity is obtainable. 

The gelatine plate so obtained may be placed in front of the 

slit of the spectroscope and the spectrum of the colour 

obtained The author has made numerous plates in this way, 

finding it an easy and efficient mode of working. 

When we examine by means of the spectroscope the light 

S 



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34 



THE THEORY OF COLOUR. 



transmitted by red glass, we find that the spectrum which is 
obtained is not a complete one compared with the spectrum 
of white light ; only the red and a part of the orange portions 
of the spectrum are visible — the remainder of the colours of 
white light have been absorbed in its passage through the 
glass. This is shown in Fig. 19, where the spectra of white 
light and red glass are compared. It will be seen that 
the red glass permits only the red, orange, and part of the 
yellow to pass, while the rest of the yellow, all the green, 
blue and violet rays are suppressed or absorbed. In connec- 
tion with the colours due to fluorescence we have seen that 

WHITE LIGHT 



RED 



A BC D 



Rirc y:l green 



fflUE 



H 



VIOLET 



RED LIGHT 

Fig. 19. 
the phenomenon is brought about by the fluorescent body 
acting on the light which falls upon it and changing its wave 
length ; hence the question may arise, May not a red substance 
act upon the light which falls upon it in such a manner as to 
change it into red light ? That this is not the case may be 
shown in several ways, as will be demonstrated in the follow- 
ing chapters ; but one simple way may be given here. If the 
spectrum of white light be thrown on a wall or screen and 
observed through a piece of red glass, we shall see the red 
portion of the spectrum, the rest being apparently eliminated ; 
if a piece of green glass be substituted for the red, then we 
shall see the green portion only, the red, yellow, blue and 
violet being absorbed or their transmission prevented ; in the 



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CAUSE OF COLOUR IN COLOURED BODIES. 35 

same way a piece of blue glass will only permit the passage 
of the blue and violet rays. It might be inferred that if the 
coloured glass exercises a degree of selection on the light 
which is presented to it, and will only allow certain rays to 
pass through, then, if red glass will stop iall but the red rays 
and green glass all but the green rays, a combination of both 
should stop all rays from passing ; this is actually the case — 
a piece of green and a piece of red glass when superposed one 
on the other will stop all light from passing through them^ 
and on looking at them will appear black in consequence. 

We have in the foregoing remarks assumed that a red 
glass only transmits red rays ; in reality it does more than 
this. If we take a spectroscope and fix across one half of the- 
slit a piece of red glass we shall see, first, an ordinary luminous^ 
spectrum, and, secondly, the spectrum of the red glass ; by 
this means we shall be able to compare the two together and 
better observe the effect of transmitting the light through the 
red glass. In the first place we shall see that the glass not 
only prevents the transmission ' of some of the colours, but 
also that the intensity of those which are transmitted is very 
considerably reduced. The reduction in intensity can be 
measured, but it is difficult to show the relative intensity by 
shading on paper. One way of doing this is shown in Fig. 20^ 
which represents the spectrum of red glass. Here the whole 
rectangle indicates the extent and intensity of the light of a 
complete spectrum. The rectangle AHNO shows the space 
occupied by the spectrum of white light, while the shaded 
portion gives some idea of the extent and intensity of the 
light transmitted by the red glass ; the height NL of this 
portion shows the relative intensity of the light transmitted 
compared with the light of the corresponding portion of the 
spectrum of white light. We see from this that while red 
glass permits the transmission of some of the red rays, it also 
allows a portion of the orange and, in a greatly diminished 



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36 



THE THEORY OF COLOUR. 



degree, the yellow rays, together with even a smaller proportion 
of the green and blue rays, to be transmitted ; but the violet 
rays are completelj^^ cut off. The degree of luminosity of the 
rays from greenish-yellow to blue which the glass transmits being 
so small, it is to the eye overpowered by the preponderance 



RED 



VEL. . GREEN BLUE 



VIOLET 




Fig. 20. — Spectrum of red glass, 
of red rays ; consequently the light from the glass appears 
red ; it is only when we view the red light through the 
spectroscope that we find that it contains yellow, green and 
blue light to a small extent. It must, however, be pointed out 
(as will be seen more fully later) that the character and extent 



R ED 



YEL. GREEN BLUE 



VIOLET 




Fig. 21. — Spectrum of orange yellow glass. 

of the rays which can be transmitted vary with different kinds 
of red glass ; some may cut off more of the green and blue 
rays than others ; and some may transmit more of the orange 
and yellow rays. Compare Plate I., in which are given the 
spectra of various red bodies. 

As another example we may take a glass of an orange- 
yellow colour, the spectrum of which is shown in Fig. 21. 



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CAUSE OF COLOUR IN COLOURED BODIES. 



37 



Here we see that the glass transmits the red, orange and 
yellow rays with a slightly diminished intensity ; the green 
with a considerable diminution of intensity, a little of the blue 
and a very small portion of the violet ; the eye sees, as it 



RED YE.L. GREEN BLUE 

T 



VI L ET 




Fig. 22. — Spectrum of green glass. 

were, the mean of these colours, therefore we say the glass is 
orange-yellow. Fig. 22 shows the absorption spectrum of a 
piece of green glass. In this case the glass materially reduces 
the intensity of the light ; this is shown by the curve barely 
extending to half the height of the normal spectrum in the 
green portion, while it tapers off towards the yellow on one 



RED 



YEL. GREEN BLUE 



V I O L ET 




Fig. 23. — Spectrum of blue glass. 

side and violet on the other. It will be noticed that the glass 
permits the violet rays (but with diminished intensity) up to 
the H line to pass, while it stops all the red. 

In Fig. 23 is shown the spectrum of a blue glass. This 
is much more complex in character than any of the others. 
Every part of the normal spectrum is represented, the green- 



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38 THE THEORY O:^' COLOUR. 

blue to violet being in considerable amount ; while a portion 
of the spectrum close to the A line in the red is shown, there 
is but little of the orange-red near the B line, a little more of 
the orange in the neighbourhood of the C line, a little of the 
yellow and somewhat more of the greenish-yellow in the space 
between the D and E lines. 

The quantity and character of the light which is absorbed 
by coloured glasses, or coloured media of any kind, depend 
upon the thickness or depth of colouring ; thus red colouring 
matter, when in a thin layer, may permit some of the green 
and even small quantities of the blue and violet rays to pass, 
in a thicker layer, with red, perhaps, some of the green rays 
may emerge ; while in a very thick layer none but red rays 
may pass. This explains how it is that the dyer, by using 
more or less dye-stuff, is able to produce so many varieties oV 
tint, varying somewhat in hue, from the same colouring 
I matter; when, for instance, only a small amount of dye-stuff 
is applied it is not in sufficient quantity to neutralise, so to 
speak, all the white light which is reflected frofia the fibre on 
which the dye-stufl* is applied ; as the quantity of dye is in- 
creased less white light is reflected, the colouring matter then 
shows its normal hue. 

Absorption Spectra of Colouring Matters. — In the practical 
applications of dy6s for the colouring of textile fabrics of all 
kinds we are accustomed to mix them together in a variety 
of ways to produce particular shades that may be desired; 
thus, for instance, a green is dyed on wool by using picric 
acid or Tartrazine with indigo extract ; the first named is a 
yellow dye-stuft*, the last a blue dye-stuff. Browns are dyed 
by uniting archil (a red dye) with indigo (a blue dye) and 
acid yellow (a yellow dye) in suitable proportions. To 
understand how these various combinations, and others of 
a similar character, can bring about the desired colour we 
must know their colour absorptive action on white light. 



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CAUSE OF COLOUE IN COLOUBED BODIES. 39 

This is done by observing their absorption spectra. On 
Plates L and III. and in Figs. 24 to 29 are given the absorption 
spectra of several of the most useful colouring matters and 
dyes. 

In Plate L, No. 2, we have the spectrum of Picric Acid. 
This shows all the red, yellow and green, and a portion of 
the greenish-blue, but the rest of the spectrum is extinguished. 
We see now that picric acid is capable of dyeing greenish- 
yellow shades because it contains the green and a portion of 
the blue as well as yellow. 

No. 3 of the same plate shows the spectrum of Tartrazine. 
This colouring matter dyes much redder shades than picric 
acid, and the spectrum shows why this is do, for while the 
red, orange, yellow and green are present, the blue and violet 
are completely absorbed. The red and green constituents of 
these colouring matters, when they enter the eye, give rise to 
the sensation of yellowish- white ; hence we perceive only the 
appearance of yellow, of a reddish tint, on account of the 
greater predominance of red and green rays over those of the 
former colour. 

No. 4, Plate I., represents the sj)ectrum of Scarlet R. We 
have here the complete extinction of the violet, blue, green 
and yellow portions of the spectrum, leaving only the red and 
the orange. As a contrast to this we' have another, red dye, 
Azorubine, shown in No. 5 ; this dye-stuff produces full 
crimson shades, and the reason is that only the red rays are 
permitted to pass through, while the rest are completely 
absorbed. 

No. 6, Plate I., is the spectrum of a light shade of Magenta. 
In this case the rays absorbed are the yellow, green and 
greenish-blue ; but in dark shades of Magenta there is more 
complete absorption, and only the extreme red rays are per- 
mitted to pass. 

In No. 7, Plate I., we have the spectrum of Safranine ; in 



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40 . THE THEORY OF COLOUR. 

this there is absorption of the yellow, green, and a portion of 
the blue rays, with partial absorption of the violet, the whole 
of the transmitted rays imparting to the eye the impression 
of a violet-red, which is the hue peculiar to Safranine. 

No. 8, Plate I., is the spectrum of Rhodamine, which dyes 
pink shades. The spectrum shows the reason of this as 
Rhodamine absorbs only yellow, green and green-blue rays, 
while the violet and red rays transmitted give rise to the 
sensation of pink to the eye. 

Another red dye-stuff, the spectrum of which is given in 
Plate I., No. 9, is Eosine, shown in a dark shade, which in- 
dicates the transmission of red, orange, and a small portion of 
the yellow. In light shades there is absorption of the green 
and greenish-blue only, the other colours being transmitted. 

In No. 10, Plate I., is shown the spectrum of Acid Green. 
The green and green-blue rays only are transmitted, while 
all the other rays are absorbed. 

In No. 11 on the same plate is the spectrum of Indigo 
extract. Here the blue, bluish-green, part of the red and 
small portions of the green and yellowish-green rays are 
transmitted, the orange, yellow and violet being absorbed. 

No. 1, on Plate III., is the spectrum of another blue dye- 
stuff, Cyanol, which dyes an extremely pretty blue. It 
shows the transmission of the green, blue, part of the violet 
and a small part of the red rays, the sum total of which gives 
rise to the sensation of blue to the eyes. 

In No. 2 of the same plate we have the spectrum of 
Aniline Blue. This shows a transmission of a portion of 
the red, some of the green, all the blue and part of the 
violet rays, while the orange, yellow and extreme violet rays 
are absorbed. 

No. 3, Plate III., is the spectrum of Methyl Violet, which 
shows the transmission only of the extreme red, part of the 
blue and part of the violet rays, the rest being absorbed. 



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CAUSE OF COLOUE IN COLOUEED BODIES. 



41 



No. 4, Plate III., is the spectrum of Iodine Green. It 
shows absorption of part of the red, orange, and yellow, and 
of the blue and violet rays. 

It is the custom of dyers to mix dye-stuffs together 
for the purpose of obtaining certain shades ; thus, for instance. 
Indigo extract and Picric Acid are employed to produce 
green. Now this green is produced, not because in the 
abstract blue and yellow produce green, but because they 
both allow green light to pass through, the Indigo extract 
absorbing the red and the yellow rays, and the Picric Acid 
the blue and the violet rays ; thus only the green rays are 



A BC 


1 1 


D 




- 


G 


H 


i 


1. 


5M^^ 


J 


fc 





NAPHTHALENE RED 

Fig. 24. 

permitted to pass. A mixture of Methyl Green and Methyl 
Violet produces a blue ; this is because blue is the colour 
common to both dye-stuffs. The Violet absorbs the green and 
yellow, while the Green absorbs the red and the violet ; thus the 
blue only is transmitted. The combination of Azorubine 
with Acid Green produces a black ; an examination of the 
spectra of the two colours shows why this is so. inasmuch as 
the Azorubine permits only the red to pass through, while 
the Green transmits only the green and blue rays. When 
both colouring matters are used together no rays pass through, 
the result is the production of a black ; this proves that black 
is the result of the absence of light, and is not produced by 
the addition of one coloured light to another. 



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42 



THE THEOEY OF COLOUE. 



Fig. 24 is the spectrum of Naphthalene Red. This pro- 
duct dyes bluish-red tints, and the reason is visible from 
an examination of the spectrum, which shows the transmission 
of the red rays, together with a little of the violet, some of the 
blue, and a small quantity of the yellow. 




DRAGONS BLOOD 

Fig. 25. 

Fig. 25 is the spectrum of Dragon's Blood, which shows 
the transmission of the red and the yellow rays, and but a 
small quantity of the green, blue and violet. 

The spectrum of Turmeric, a yellow dye-stuff which 
produces somewhat orange shades, is shown in Fig. 26. 




TURMERIC 

Fig. 26. 

Here we see that yellow forms the principal portion of the 
transmitted rays ; some of the red and the lighter greenish- 
yellow rays are also transmitted. 

Figs. 27 to 29 show the absorption spectra of certain 
alcoholic solutions of various colouring matters. Alizarine, 



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CAUSE OF COLOUE IN COLOUKED BODIES. 



43 



T'ig. 27, shows transmission of the red, orange and yellow, 
with a little of the green and but a small quantity of the 
l^lue and violet. The sister colour, Purpurin, which dyes 
somewhat bluer shades than Alizarine, has the absorption 




yALIZARIN IN ALCOHOL 

Fig. 27. 

spectra shown in Fig. 28. Cochineal solutions, Fig. 29, show 
the transmission of red and blue rays, while only the green 
are absent to any extent. 

The principal difficulty in colour phenomena is to account 
for the production of such shades as browns, olives, greys 




PUR PURINE IN ALCOMOL 

Fig. 28. 

and similar shades, which often pass under the term of 
tertiary colours. An examination of the absorption spectra 
of such shades solves the difficulty. For instance, Bismarck 
Brown, which dyes cotton in reddish-brown or orange-brown 
shades, has a spectrum which shows both red, orange-yellow 
and green shades, this spectrum being very similar to that 



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44 



THE THEOEY OF COLOUR. 



produced by an orange colour; there is, however, much 
more diminution in the intensity in those portions of the 
spectrum, in other . words, the luminosity of the spectrum of 
Bismarck Brown is much less than that of an orange dye ; 




COCHINEAL IN ALCOHOL 

Fig. 29. 

we may regard Bismarck Brown as a poor or degraded orange 
without much error. 

It is a common feature in dyeing to produce olive by 
using a mixture of Acid Green and Orange G. If the 
spectrum of the olive colour is examined, it shows only a 




VERMILION 

Fig. 30. 

small portion of the green in very diminished intensity; 
therefore we may regard olive as a degraded green. 

Greys are produced in dyeing by mixing red, yellow and 
blue dye-stuffs in various proportions. When the spectra 
of these shades are examined they usually show the presence 
of two points of light, one in the red and the other in the 
bluish-green. Now red and green together produce the 



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CAUSE OF COLOUR IN COLOURED BODIES. 



45 



sensation of white; but owing to the considerable degree 
of absorption there is a very low luminosity, which appears 
to the eye as a grey ; its production in this way is equivalent 
to mixing a black and white together, the shade of grey 



A BC D 1 


E 1 


= G H 


1^ 


^ 


^^ 




— 






CAR 


Ml NE 





Fig. 31. • 

produced depending on the relative proportion of the dyes 
used. 

Pigments, also, give absorption spectra, which may be 
exhibited in two ways, either by the light that is reflected from 
them, or by the light that is caused to pass through a thin 




INDIAN RED 

Fig. 32. 
layer of the material. In either case, similar spectra are 
obtained. Figa 30 to 42 show the spectra of the most 
common pigments used by painters. In Fig. 30 we have that 
of VermiUon, which shows that this pigment reflects the 
red and yellow rays and a small proportion of the other 
colours. In Fig. 31 we have that of Carmine, which differs 



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46 



THE THEOEY OF COLOUB. 



from that of Vermilion in there being a larger proportion of 
blue and violet rays ; to which circumstance is due the 
crimson hue of Carmine. In Fig. 32 is given the spectrum 
of Indian Red. In this the red, orange and yellow rays 
are transmitted, also a small proportion of the blue and 




EMERALD 



EEN 



Fig. 33. 
violet rays. It is somewhat of interest to compare the 
spectrum of Vermilion with that of Indian Red ; the former 
pigment is of a bright scarlet colour, while, the latter has a 
dull reddish hue. The spectra show that, while in the case of 
the Vermilion, the red and orange rays are transmitted in 




CHROME GREEN 

Fig. 34. 
almost their full intensity, in Indian Red there is a very 
considerable loss in intensity in these rays, and it is to this 
circumstance that the much duller colour of that pigment is 
due. In Fig. 33 is given the spectrum of Emerald Green, 
from which it will be seen that while the green rays are 
present in almost their full intensity, there are present small 



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CAUSE OF COLOUE IN COLOUEED BODIES. 



47 



proportions only of the other rays of the spectrum. In Fig 
34 is given the spectrum of Chrome Green, where we have 
the green rays in nearly their full intensity, but there is 
also reflected a portion of the red rays and some of the blue 



A BC D 




H 



TERRA VERTE 

Fig. 36. 

and violet rays, and it is to the presence of these latter shades 
that we must ascribe the duller tone of Chrome Green in com- 
parison with Emerald Green. In Fig. 35 we have the 
spectrum of Terra Verte ; this colour is more renowned for 
its permanence than for its brilliancy. Its hue is that of a 




CHROME YELLOW 

Fig. 36. 

greyish-green ; from the spectrum we gather that while the 
green rays are present, there is also a fair proportion of the 
red, orange and yellow rays as well as a little of the blue and 
violet rays ; the intensity of all these rays is, however, very 
slight; this low intensity and the combined action of the 



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48 



THE THEOEY OF COLOUR. 



blue and i*ed rays, when viewed by the eye, cause Terra 
Verte to appear of a greyish hue. 

In Fig. 36 we have the spectrum of Chrome Yellow. It 
shows that this pigment reflects a large proportion of the 




CADMIUM 



YELLOW 

Fig. 37. 



y^ellow and green rays, with a small quantity of orange 
and blue. Cadmium Yellow is a pigment, of a rather more 
orange tone than Chrome Yellow. This fact is explained 
by examination of its spectrum, given in Fig. 37, which shows 




YELLOW OCHRE 

Fig. 38. 

that, while yellow rays are strongly represented, there are also 
more violet and red ra,ys than in Chrome Yellow. 

The spectrum of Yellow . Ochre is seen in Fig. 38, which 
shows the presence of yellow, some red, and a little green ; 
the intensity of the rays is small as compared with Chrome 
Yellow, and to this fact the dull hue of Yellow Ochre is to be 



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Plate IV. 

Al Dl 




(Theory of Colour). Effect of Mixing Colours. 



To face p, 48. 



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CAUSE OF COLOUE IN COLOUEED BODIES. 



49 



ascribed, while the greater proportion of red reflected accounts 
for its reddish hue. 

In Fig. 39 we have the spectrum of Ultramarine, a pigment 
of a bright hue. We see that, while there is a small quantity 
of the red and yellow rays, there is a great predominance of 



A BG 




ULTRAMARINE 

Fig. 39. 

the blue and violet rays to which the colour of the pigment 
is due. 

Ultramarine Green is shown in Fig. 40, where we see the 
green rays are in the greatest predominance, while there is 



A BC 




ULTRAMARINE GREEN 

Fig. 40. 

only a small proportion of the blue and orange rays of a low 
intensity. 

In Fig. 41 we have the spectrum of Smalt, which is a 
blue pigment of a violet hue and low intensity. The 
spectrum shows that almost every ray of colour is present 



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50 



THE THEOBY OF COLOUR. 



in greater or less quantity, and that the red, the blue and 
the violet rays are much more prominent than the other 
rays. The blue colour of this pigment is evidently due to 
the fact that the red and green on the one hand, and the 




SMALT 

Fig. 4^1. 

blue and yellow on the other, are present in just the propor- 
tions required to produce white light, leaving the violet and 
a portion of the blue to impress themselves on the eye. The 
low intensity of the colour is due to only a portion of each 
colour being transmitted. 




PRUSSlAISf 



BLUE 

Fig. 42. 



The well-known pigment, Prussian Blue, has a[spectrum 
(Fig. 42) of a different character to either Ultramarine or Smalt. 
In this the blue and green rays have a greater predominance, 
the violet is also present, but there is little of the yellow or 
red rays. The deep colour of Prussian Blue is undoubtedly 



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CAUSE OF COLOUK IN COLOUBED BODIES. 



51 



due to the fact thai the principal rays are transmitted in 
almost their full intensity. 

We may conclude this section of the subject by an 
examination of the green colouring principle to which 
vegetation owes its hue, i,e. Chlorophyll. An examination of 
the spectra of the green colours which have already been 
given will show that with them the red is absent or nearly 
so, and the blue and violet are present in very small quantities. 
In Chlorophyll, however, we have a different result : we find 
the extreme red of the spectrum present in almost its full 
intensity; the orange is nearly absent, while the yellow, 




CHLOROPHYLL 

Fig. 43. 

greenish-yellow and green, are present in considerable 
amount, a small proportion of the blue and violet rays being 
also included (see Fig. 43). The hue of Chlorophyll presents 
itself to the eye as a yellowish-green, and the reason of this 
is that the red and a portion of the green combine to form 
white light, the remainder uniting to produce a shade of 
yellowish-green. The fact that the Chlorophyll of green 
leaves reflects some of the red rays may be seen in the foliage 
of trees, when illuminated by the setting sun, having a 
reddish appearance. 

The study of absorption spectra such as those above 
described leads to one very important conclusion: that the 



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52 THE THEOBY OF COLOUR. 

eye cannot distinguish the true character of any light, white 
or coloured, which may be presented to it, but observes them 
one and all as monochromatic in effect, although they are 
possibly polychromatic in structure. 

It is a fact well known to painters that the appearance 
of a pigment depends very greatly upon the particular vehicle 
or medium in which it is disseminated ; this may be proved 
by an examination of drawings made in crayons, water 
colours and oil, using the same pigment. The explanation of 
this phenomenon is to be sought in the different manner in 
which the pigment or paint surface reflects the light that falls 
on it ; in the case of a crayon drawing, and to a limited 
extent a water-colour painting, there is not only reflected the 
characteristic colour of the pigment, but a good deal of white 
light, the presence of which materially modifies the hue of the 
pigment as it is seen by the eye ; in the case of water colours 
the presence of the very small proportion of gummy matter 
which is employed to fix the pigments is found to consider- 
ably reduce the quantity of white light which the pigment 
reflects, therefore we are much nearer to obtaining the true 
hue of the pigment, but there is less light reflected on the 
whole. When oil or varnish is used as the. vehicle, the pig- 
ments appear to be much darker, the colour is richer, and 
there is found to be less white, light reflected from the pig- 
ment. This change in appearance is due to the different con- 
ditions in which the light falls upon and is reflected from the 
pigment. With the dry pigment, as in crayon work and 
chalk drawings, there is a very considerable amount of white 
light reflected from its surface together with the characteristic 
colour rays, owing to the difference in the density of the air 
in which the light moves, and the surface from which it is 
reflected. In the case of water colours, or pigments immersed 
in water, the conditions are somewhat different, the light 
moving in a dense medium and being reflected from a pigment 



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CAUSE OF COLOUR IN COLOURED BODIES. 53 

which is in one sense only slightly more dense than the 
liquid ; hence there is but little white light reflected, and 
the coloured light which is reflected is distinctly purer, the 
appearance of the pigment becoming richer. In the case of 
paintings in oils we have a medium which is of the same 
-density as the pigment, consequently there is very little white 
light reflected from its surface, therefore the colour appears 
-darker. This is particularly noticeable with Prussian Blue, 
which, used by itself in oil, appears of a blue-black colour ; it 
is only when spread out in very thin layers on a white 
surface, or mixed with a white pigment, that the proper blue 
hue of Prussian Blue manifests itself. This change of colour 
is also noticeable with other pigments : ochres or natural 
earths, which appear of a pale hue in the dry state, when 
mixed with oil seem much darker and more richly tinted. 

This change in appearance of pigments when mixed " with 
media has a very important influence on their use in painting, 
so that between the extremes of drawings in crayons and 
<;halks and oil painting we have various intermediate 
-qualities. In oil painting the colouring is characterised by 
its richness and the transparency and depth of the shadows ; 
while in crayon drawing the colours obtained are much paler, 
the shadows are much less intense, while a harshness pervades 
the whole drawing. 

In fresco drawing or painting the artist is troubled by this 
change of appearance of pigment due to the difference of con- 
ditions in the media, for he has to work with a wet medium, 
which imparts to the pigments considerable depth of colour, 
while the finished picture is observed when the medium has 
evaporated, consequently its effect on the pigments is lost, the 
colours then having lost much if not all their brilliancy. The 
artist has necessarily to be on his guard to make allowance 
for this change, which renders fresco painting one of some 
difficulty; for this reason few artists are successful in pro- 



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54 THE THEOKY OF COLOUK. 

ducing fresco drawings which are wholly satisfactory as 
regards harmonious colouring and uniformity of hue. 

We may assume from the study of the absorption spectra 
of pigments, etc., that coloured bodies owe their colour to the 
selective power they exert on the rays of light which fall upon 
them, quenching or absorbing some, reflecting or transmitting 
others ; the colours which they show depending upon the char- 
acter and intensity of the rays which are transmitted. 



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CHAPTER III. 

COLOUR PHENOMENA AND THEORIES. 

Dyers, painters and others who use colouring matters of 
various descriptions are well aware of the fact that, by the use 
of a few of these colouring matters, they are able to. produce a 
great variety of colour effects : thus, for instance, the painter 
with red, yellow and blue pigments, can produce a great variety 
of other colours and tints. The same may be said of a textile 
colourist ; for instance, by mixing a red and a yellow, orange 
can be produced, but by using these two colours in various pro- 
portions he can produce an infinite variety of tints of orange, 
ranging from an extreme orange-red to a very yellowish- 
orange. Again, by mixing a blue and a yellow together, 
an infinite variety of green shades, from a yellowish-green to a 
bluish-green, may be produced ; while the admixture of blue 
and red in various proportions will produce various tints of 
purple and violet ; then by mixing the three colours, red, blue 
and yellow together an infinite variety of olive, sage and brown 
shades (which are known to the painter as sad shades) or 
even black may be produced. This fact, known to colour- 
ists for many years, formed the foundation for that theory of 
three primary colours — red, yellow and blue — which owing to 
the fact that Dr. Brewster was the principal exponent of it, 
has been known as the Brewsterian theory of colours. He 
considers that there are three fundamental colours, — red, 
yellow and blue — and that by the admixture of these three 

colours all other colours can be produced. This theory has, 

(55) 



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56 



THE THEOEY OF COLOUR. 



however, been shown by several physicists — Thos. Young, 
Helmholtz, and others — to be erroneous, it has therefore given 
place to a much more correct theory, although we may say in 
defence that it explains very well the phenomena which occur 
on mixing colouring matters together. 

Before passing on to the consideration of theories of colour, 
it may be well to consider some of the results that are obtained 

by mixing various colours to- 
gether. In mixing colours 
it is well to distinguish be- 
tween the mixture of colour- 
ing matters, dyes and pig- 
ments, and the mixture of 
coloured lights. It will be 
more convenient to deal with 
the latter phenomena first, 
noting the effects which can be 
produced by mixing coloured 
lights, and the means by 
which these colour mixtures 
can be produced. 

One very well - known 
method of making experi- 
ments with mixtures of col- 
oured lights is by means of a revolving disc, the experiment 
being that of Newton s disc, with which every student of light is 
familar. A white cardboard disc is painted in segments with 
different colours along its radius (Fig. 1, Plate II.), on rotating 
this rapidly, by the influence of the phenomenon known as 
persistence of vision (which will be fully discussed in the 
chapter on the physiology of light), the colours blend into 
one another, and a uniform whitish or greyish-white colour 
is produced. 

Fig. 44 represents a very convenient rotatory apparatus. 




Fig. 44. 



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COLOUR PHENOMENA AND THEORIES. 



57 



■consisting of an electro-motor driven by a galvanic battery of 
^ny convenient kind. The discs of cardboard are attached to 
the spindle of the electro-motor, which is so arranged that 
they may be changed as required. Fig. 45 is a drawing of 
Rothe's apparatus for rotating the colour discs. In this appar- 
atus a variety of speeds may be obtained, varying from slow 
to very quick, by driving as may be desired, from the puUeys 
1, 2 or 3 : if 3 be made the driving pulley, then a slow speed 
is obtained; if No. 1 is used, then a quick speed is the result. 
If, instead of the Newton's disc, a disc painted one half blue and 
the other half yellow is employed, on rotation we shall obtain 
the Sensation produced by mixing blue and yellow lights to- 




FiG. 45. 

•gether, that is a white and not a green. The white may not, 
however, be quite pure, but may be more or less tinted with 
blue or green, because it is extremely difficult to proportion 
•exactly the blue and yellow in this method of working. A 
better plan is that devised by Maxwell, who took two or more 
discs, each painted with a desired uniform colour ; then, by mak- 
ing in each a slit from the centre to the edge, he was able, as 
shown in Fig. 46, to place them together and produce a com- 
bined disc showing any desired proportions of colour ; thus it 
is possible, when using blue and yellow, either to expose more 
yellow or more blue, as the results on rotating the disc show to 
be desirable. Fig. 47 shows the rotatory apparatus with these 
discs in position ; with their aid it is quite possible to study 



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68 



THE THE OB Y OF COLOUR. 



combinations of two, three, or even more colom's. By chang- 
ing the proportion of blue to yellow a position is reached whei> 
on rotation we obtain a greyish- white ; whatever the pro-^ 




Fig. 46. 

portions of the blue and yellow in these experiments, in no- 
case is a green obtained. 

Another method of combining coloured light is to place 




Fig. 47. 



two sheets of the desired colours side by side on the table, and 
then to place a sheet of glass upright between the two patches- 
of colour ; on looking through the glass at one of the patches. 



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COLOUE • PHENOMENA AND THE6BIES. 59 

we also see the reflection of the other, the sensation visible to 
the eye, however, is not that of the two colours separately,, 
but the combined sensation of the two. By changing the 
position of the patches it is quite possible to view them as 
though they overlapped, we are then able to see the effect 
of the colours being combined together as well as separately ; 
in the case of blue and yellow patches, white is always the 
result of the union. 

Another method of mixing colours is by means of Dove's 
dichroiscope, a section of which is shown in Fig. 48. This 
consists of a box, ABCD, with an open back, ED, in which 
can be fixed a piece of .coloured glass, and an open top, AB,. 




on which a pieciB of coloured glass may also be placed ; while- 
arranged diagonally from the front to the back are a number 
of glass plates, CB. If now the eye be placed at the aperture^ 
E, coloured plates being on the top and at the back of the box, 
then the light passing from the mirror, M, through the glass,. 
BD, and direct through the glass plates, BC; the light which 
passes through AB will at the same time be reflected from the- 
surface of the plates, BC, and will also reach the eye, so that 
the eye receives two colour sensations, one from BD, the other 
from AB, but, as it is impossible to distinguish the two, one 
colour effect only will be observable — what this colour effect 
is will depend upon the colours of the two glass plates; not 
only so, but also upon the relative proportion of the two- 



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60 THE THE OK Y OF COLOUK. 

'Colours. By taking advantage of the fact that the light 
passing through the instrument is more or less polarised, then 
by observing through a Nicol's prism, P, instead of direct, we 
can adjust the relative proportions of the two colours. By 
jTotating the NicoFs prism more or less we find that, for 
instance, red and green glass will infallibly give a yellow 
varying from orange-yellow to greenish-yellow, according to 
the proportions of the red and green. Blue and yellow glasses 
give white, green and purple give alsO white, red and yellow- 
give orange, green and yellow yellowish-green, and blue and 
red purple to violet, the tints of the mixed colour depending 
upon the hues of the glasses which are employed; a little 
•care is, however, needed in selecting the glasses to give the 
best possible efiects. 

Advantage may also be taken of the fact that calcspar is 
•double refracting and therefore gives two images of an object 
of equal intensity ; if now a small screen of cardboard has two 
small apertures cut in it, these apertures can be covered with 
pieces of stained glass ; these viewed through an achromatic 
prism of calcspar, yield two images of each glass, four images 
altogether. By careful arrangement it is possible to arrange 
for one image from the two glasses to fall on the same spot ; 
then we get the colour eflect of the two colours combined, 
while there are also, separate images of each colour for com- 
parison. The colour effects so obtained are the same as given 
>by Dove's dichroiscope described above. 

For showing colour phenomena on a large scale two optical 
lanterns may be employed, both arranged so as to be focussed 
•on the same portion of the screen, while the use of stained 
glass or coloured gelatine films will give the desired results. 

The following are a few results which the author has 
obtained on experimenting with Maxwell discs! Using ultra- 
marine and a deep yellow disc in equal proportions, combina- 
i:ions which have a reddish hue were produced ; altering the 



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COLOUR PHENOMENA AND THEORIES. 61 

proportion to 150 of ultramarine and 210 of deep yellow, a 
reddish-white tint appeared. If, in place of a deep yellow, we- 
use a pale shade of yellow, then, if the proportions of the two- 
discs are equal, a creamy-white is obtained, while with 270* 
parts of ultramarine and 90 parts of chrome a pale violet tint 
is produced. A mixture of 180 of vermilion and 180 of 
ultramarine produces a lilac rose tint, while 270 of vermilion< 
and 90 of ultramarine gives a pinkish-red ; or, if the propor- 
tions be reversed, 90 of vermilion and 270 of ultramarine, a 
blue-violet is produced. Using a mixture of 250 parts of 
Prussian blue and 110 of pale chrome we obtain a grey of a 
faint greenish tint. A disc of vermilion and green in about 
equal proportions produces a tint of a yellowish cast. In* 
using these mixtures a great deal depends upon the depth of 
tone of the vermilion disc and that of the green disc, so the- 
shade of the combined results may vary from yellowish to a 
pale brown. If the vermilion disc is in excess then a terra- 
cotta shade is obtained, while if the green disc predominates 
the hue becomes greenish ; a combination of a vermilion disc 
with a yellow disc in equal proportions produces a deep orange 
shade, while if the vermilion predominates, an orange-red 
appears ; vermilion and Prussian blue discs in equal propor- 
tions produce a dull greenish shade — an excess of the Prussian* 
blue produces a deep lilac, while an excess, of the vermilioni 
produces a pale red. A disc of vermilion and one of emerald 
gre'en produces a whitish-yellow ; this of course is the result 
according to Young's theory. A disc painted with violet and 
one with yellow give a yellowish-grey, while a combination 
of a violet disc and a dark-green disc gives a greenish-grey. 
A disc coloured with carmine combined with one painted with 
green gives rise to a faint reddish tint. 

The results thus produced are due to the effect of persist- 
ence of vision, while the pigments used are not pure colours 
(see the spectra Figs. 30 to 42), it is not to be expected that< 



/ 



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62 THE THEOEY OF QOLOUB. 

the results of these colour experiments should be exactly 
those demanded by theory ; they are vitiated by what may be 
termed errors of experiment. They show how wide is the 
difference between mixing the colour sensations themselves 
and mixing the pigments or colouring matters which have 
been used in the production of the discs ; thus, a mixture of 
ultramarine with chrome yellow on the discs produces a 
reddish-white, while the same pigments mixed together 
produce greyish-green. Prussian blue and chrome yellow 
discs give a greenish-grey, a mixture of the two pigments 
gives a full green ; vermilion and emerald-green mixed by 
the disc produce yellow, while in the form of pigments they 
give rise to a brick red Vermilion and ultramarine mixed 
together by the discs give a faint rose tint, while as pigments 
they give rise to a purple colour. 

We may also compare the results which are obtained by 
mixing coloured lights together with the Dove apparatus, 
with the calcite prism, and we may also compare these results 
with the effect produced by passing light through the two 
glasses and observing them with the eye. Thus a red glass 
and a green glass observed by the prism give rise to a pale 
yellow or to an orange colour according to the character of 
the red glass, while on looking through the two glasses placed 
together the colour appears dark-green to black. A yellow 
glass and a blue glass viewed with the prism appear white, 
which may possibly have a pinkish hue according to the exact 
tone of the two glasses ; by direct observation these glasses 
appear to be green. A mixture of red and blue glass appears 
of a purple or violet in the apparatus, and of a deep red directly. 
Yellow and red glasses appear to be yellow or orange with 
the prism, and of a deep orange or red seen directly. A 
yellow and a blue-green glass with the prism appear of a 
yellowish-white colour, without, of a rjcb yellowish-green. 
A violet and a green glass with the prism may have a blue 



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COLOUR PHENOMENA AND THEORIES. 63' 

<5olour, while without the prism they would appear to be 
black. From these results it . will be seen that the effects 
obtained by mixing coloured pigments together, and those 
obtained by mixing coloured lights, are of a very different 
order. The difference is very marked in many cases, and the 
results obtained in one cannot be predicted from the other. 
Figs. 2, S et seq., Plate II., show some of the results obtained 
with coloured lights which are allowed to fall one upon the 
other on a screen from two lanterns, and the colour obtained 
by two coloured glasses placed together in a beam of light. 
In Fig. 2, Plate II., we have the result of two discs, one of 
blue the other of yellow light, • falling upon the screen from 
two lanterns — where they overlap it appears white. In Fig. 
4 we have the same two colours thrown together on the screen 
from one lantern — where they overlap it is green. These differ- 
ences of result are explainable in this way : In the first case 
ive have both blue and yellow lights illuminating the same 
«pot, and the illumination excites in our eyes the sensation of 
white. In the second case the light has already passed 
through one glass, say the blue, and been robbed of its red 
and yellow rays before it passes through the yellow glass, and 
this again exerts its absorbing effect, stopping the passage of 
the blue and violet rays which reach it, only permitting the 
^reen rays to pass through, so that green alone appears on 
the screen. In the second place we have in Fig. 3, Plate II., 
the effect of two discs, one of red the other of green light 
from two lanterns — where they overlap it appears yellow. 
This of course is in accordance with Young's theory of light. 
In Fig. 5, Plate II., we see the effect of the light passed 
successively through the red and green glasses, the result 
being the production of black. This is due to the fact that 
the red glass, through which the light first passes, permits 
only the passage of red rays, these on reaching the green 
glass are absorbed, black appearing as the result. 



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64 THE THEOKY OF COLOUR. 

So far we have considered the mixture of colour sensations^ 
produced by transmission or reflection from artificial colours ;: 
it will now be as well to briefly describe the results obtained 
by mixing together coloured lights of a pure character, such 
as are got by means of either the spectroscope or the polari- 
scope. It is quite possible to produce a spectrum by one spec- 
troscope, and to project upon this any portion of a spectrum 
produced by another spectroscope ; by an arrangement of the 
polariscope, as shown previously, overlapping images of two 
colours can be produced. Captain Abney has described an 
arrangement by means of three slits, which, placed in con- 
nexion with the spectroscope, is capable of allowing three 
portions of the spectrum to fall upon the screen at one spot. 
The apparatus can be so arranged that any portion of the 
spectrum can be examined at the same time ; if with such an 
apparatus the slits are arranged in the red, the green and the 
violet, we have white light produced. If now the slit in the 
green is moved towards the red the tint of the mixture be- 
comes more reddish ; to still keep it white the slit in the red 
must be partially closed, until we find that, by having one slit 
on the yellowish-green and the other slit on the violet, we 
also are again able to produce white light. This fact tends ta 
show that the yellowish-green rays are formed by the ad- 
mixture of the red "and the green of the original spectrum ; it 
is also found that a mixture of red and a bluish-green produces- 
white. In a similar manner we find that a mixture of orange 
and greenish-blue makes white, a mixture of yellow and blue 
makes white, a mixture of greenish-yellow and violet makes 
white, and of green and purple makes white. Putting these 
results in the form of a table for clearness, we have the 
following five combinations, any of which will produce 
white : — 

Red and bluish-green. 

Orange and greenish-blue. 



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Plate v. 




(Thboby of COLOUt). 



Colour Cootrasts. 



Tffaeg p. 64. 



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COLOUK PHENOMENA AND THEOBIES. 65 

Yellow and blue. 

Greenish-yellow and violet. * 

Green and purple. 

In other words, white light must contain one of these five 
pairs of colours, in each case one colour is said to be complemen- 
tary to thp other, but these same results are obtained whether 
we use the spectrum lights or the lights of the polariscope. 

The changes brought about by one colour falling upon 
another is of very great importance, it has some bearing on the 
eniployment of pigments and dyes in the production of paint- 
ings and designs for decorative purposes. Thus Rood has 
made a number of experiments on this question, and we may 
give his results here, in several cases they have been repeated 
by the author. 

. TABLE I. 

Yellow light falliug on paper painted with 

^ Cannine gave . . . • Bed-orange. 



Vermilion gave 
^ Orange ^ gave . 
. - Chrome yellow gave 
^ Gamboge gave 
^* YellowiSh-green * gave 
^ Green ' gave . 
. Blue-green * gave . 
T Cyan blue * gave 

Prussian blue gave 

Ultramarine blue gave 

Violet * gave . 

Purple ' violet gave . 

Purple 8 gave . 

Black * gave . 



Bright orange-red. 

Bright orange-yellow. 

Bright yellow. 

Bright yellow. 

Yellow. 

Bright yellow-green. 

Yellow-green (whitish)* 

Yellow-green. 

Bright green. 

White. 

Pale reddish tint. 

Orange (whitish). 

Orange. 

Yellow. 



^ Mixture of red lead and Indian yellow. 
^ Mixture of gapiboge and Prussian blue. 
3 Mixture of emerald green with a little chrome yellow. 

* Mixture of emerald green with a little cobalt blue. 
^ Mixture of cobalt blue and emerald green. 

* Hoffmann's violet BB. "^ Hoffmann's violet BB and carmine. 
® Hoffmann's violet BB and carmine. ^Lamp black. 

5 



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66 



THE THEOBY OF COLOUR. 



TABLE II. 



Red light falling on paper painted with 
Carmine gave . 
Vermilion gave 
Orange gave . 
Chrome yellow gave 
Gamboge gave . 
Yellowish-green gave 
* Green gave 
Blue-green gave 
Cyan blue gave 
Prussian blue gave . 
Ultrckmarine blue gave 
Violet gave 
Purple violet gave . 
Purple gave . 
Black gave 



Red. 

Bright red. 

Red-orange and scarlet. 

Orange. 

Orange. 

Yellow and orange. 

Yellow and orange (whitish). 

Nearly white. 

Grey. 

Red-purple or blue-violet. 

Red-purple or blue-violet. 

Red-purple. 

Red-purple. 

Purple-red or red. 

Dark red. 



TABLE III. 



Green light falling on paper painted with 



Carmine gave . 
Vermilion gave 
Orange gave . 
Chrome yellow gave 
Gamboge gave . 
Yellowish-green gave 
Green gave 
Blue-green gave 
Cyan blue gave 
Prussian blue gave . 
Ultramarine blue gave 
Violet gave 
Purple violet gave . 
Purple gave . 
Black gave 



Dull yellow. 
- Dull yellow or greenish-yellow. 
Yellow and greenish-yellow. 
Yellowish-green. 
Yellowish-green. 
Yellowish-green. 
Bright green. • 

Green. . 
Blue-green. 

Blue-green, cyan blue. 
Cyan blue, blue. 
Cyan blue, blue, violet-blue. 
Pale blue-green, pale blue. 
Greenish-grey, grey, reddish-blue. 
Dark green. 



TABLE IV. 



Blue light falling on paper painted with 
Carmine gave . 
Vermilion gave 
Orange gave . 
Chrome yellow gave 
Gamboge gave 
Green gave 



Purple. 
Red-purple. 
Whitish-purple. 
Yellowish-grey, gpreenish-grey. 
Blue-grey. \ 

Blue-green, cyan blue. 



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COLOUR PHENOMENA AND THEORIES. 67 



Blue-green gave 
Cyan blue gave 
Prussian blue gave . 
Ultramarine blue gave 
Violet gave 
Purple violet gave . 
Purple gave 
Black gave 



Blue, cyan blue. 

Blue. 

Blue. 

Blue. 

Ultram&rine, violet-blue. 

Blue-violet. 

Violet-blue, purple-violet. 

Dark blue. 



Incidentally there have been mentioned some of the colours 
which can be produced by the admixture of various pigments 
together. It will be as well if we devote more attention to 
this question and at the same time to the colours obtained by 
the dyer in mixing various dye-stuffs together. For instance, 
when chrome yellow and vermilion are mixed an orange is 
produced; when a yellow pigment and a blue pigment are 
mixed together a green is the result — this is noted with 
Prussian blue^ and gamboge, a very favourite mixture with \y 

artists; or Prussian blue with chrome yellow, which forms 
the Brunswick green of the house painter. The reason of a 
blue and a yellow pigment producing green and not white, as 
would have been the case with blue and yellow lights, is that 
Prussian blue reflects green light as well as blue light, which 
may be seen from its spectrum given on page 50, while the 
chrome yellow, as will be noted from its spectrum given on 
page 67, also reflects green as well as yellow. 

In explaining this effect, it is usually stated that the blue 
rays of the one pigment and the yellow rays of the other pig- 
ment neutralise one another, allowing only the green rays to 
develop themselves, but it is really due to the combined 
absorptive action of the pigments on the light resulting in 
only the green rays being allowed to pass or reflect that the 
mixture of yellow and blue pigments produces green. When 
red and yellow pigments are mixed together, orange is the 
result,. as stated above; in this case a similar result is ob- 
tained, inasmuch as we not only get an absorptive effect of the 



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68 THE THEOBY OF COLOUE. 

two pigments on the light, the red absorbing all the rays 
from the violet to the green, and most of the yellow; the 
yellow pigment absorbing all the rays from the violet to the 
bluish-green, and most of the red — thus orange itself, part of 
the red and part of the yellow are the only rays not absorbed, 
the combined effect of red rayS and yellow rays upon the eye 
is to produce orange, therefore orange is the predominating 
colour. 

Again, when blue and red pigments are combined together, 
violet is the result ; here again, as with the orange combina- 
tion, we have not only the absorptive effect of the two pig- 
ments on the light, cutting off" all but red, blue and violet, but 
also the physiological effect, inasmuch as when red and blue 
rays are both present they give rise to the sensation of 
violet. 

But the character of the orange, green or violet which 
is produced largely depends upon the character of the red and 
yellow, yellow and blue, red and blue pigments which are 
used, as also upon the relative proportions of those which are 
present. Ultramarine, although a blue pigment, does not 
yield as good greens as Prussian blue ; its tone approaches 
more nearly to a pure blue than that of Prussian blue, there- 
fore it does not reflect so many of the green rays (see Figs. 
39 and 42). Yellow ochre, again, does not produce good greens, 
but greyish tones. Carmine produces purer violets with 
Prussian blue than can be obtained with vermilipn, because it 
reflects more of the violet rays than the latter pigment, as 
may be seen by a comparison of the spectra given in Figs. 30 
and-31. 

If a red pigment and a green pigment are mixed together, 
a brown is the result, this varying in tone or hue according to 
the relative proportions of the two pigments ; brown is there- 
fore really a resultant of a double effect, first the red and the 
green tending to absorb nearly the whole of the rays, only 



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COLOUR PHENOMENA AND THEORIES. 69 

permitting the red, orange and yellow to pass, but besides this 

there is a considerable decrease in the luminosity of the mix- /-^ 

ture, which has the effect of adding black, the result is that 

the colours are toned down, brown being produced. Mixing 

an orange and a green pigment has a similar effect, only the 

mixture is not so dark. 

The dyer, like the painter, produces a great many of his 
effects by mixing various dye-stuffs together. Thus he gets 
brown by mixing a red, a yellow and a blue dye together, 
and by varying the proportions he can produce a great range 
of shades. By using Archil, Turmeric and Indigo extract he 
gets a brown, and a similar brown is got from Indian yellow, 
Aniline blue, and Orange 2 ; it is to be noted that the orange 
or yellow predominates in each case — by increasing the pro- 
portion of the blue, the brown becomes darker. The dyer / 
is also accustomed to produce greys by mixing a red, a blue, 
and a yellow dye, as for instance a grey is obtained from 
Chromotrop 2R, Cyanine B, and Azo yellow. A spectroscopic 
examination of this mixture would show that together they 
absorb all the rays of the spectrum, for each acts so as to take 
out its own section of the rays, and therefore black results ; 
the white of the fabric dilutes this to a grey effect. By in- . 
creasing the proportion of the red, reddish-greys are obtained, 
while if the blue is increased then bluish-greys result, or if 
both the blue and the yellow are increased then a greenish- 
grey is obtained. Like the painter, the dyer gets his greens 
by mixing blue and yellow dyes together in various propor- 
tions, and occasionally he adds a little red for such colours as 
peacock green; thus, by using a mixture of Cotton blue. Acid 
yellow and Chromotrop, a peacock green can be dyed. Many 
of the modem coal-tar blacks have a bluish or violet shade ; 
it is found that, by using a little yellow or green dye, the black 
is improved and becomes much purer. This is due to the fact 
that the addition of the yellow or green dye results in the 



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70 THE THEOBY OF COLOUE. 

absorption of the blue light which the original dye-stuff 
allowed to pass through. Black can be dyed on wool by 
using a mixture of Naphthol blue, Indian yellow and Naphthol 
green : this black is produced as the result of these dyes 
absorbing the whole of the spectrum, and in allowing no rays 
to be reflected or transmitted. It is of course impossible to 
describe or to notice all the colour effects which may be ob- 
tained or produced by the admixture of different colouring 
matters, but it may be stated here that the dull effect of such 
dark shades as browns, olive-greens, etc., is due to their low 
reflecting power for light ; on the other hand, in the case of light 
tints such as greys, lilacs, pinks, creams, we have the fibre, or 
rather the light reflected from it, also playing a part in the 
sensation developed in the eye. We shall have further to 
consider the effects brought about by changing the luminosity 
of light either by an increase or a decrease thereof. 

The same colour may be produced by combining different 
dj^e-stuffs together ; thus, for instance, a bright green may be 
got with indigo extract and Naphthol yellow, and also by 
using Naphthol yellow, Orange G and Acid green, but it does 
not follow that, although the tint of the two colours may be 
the same, they have quite identical properties ; thus if sub- 
jected to various illuminants they may show slight differences 
of tints, and again the addition of other colouring matters may 
produce divergent effects; thus, while the addition of a red 
dye-stuff to one of the mixtures may produce a deep brown, 
with the other it may form a maroon. Again, the shade of 
blue produced on wool by indigo extract may be matched by 
daylight with a mixture of Naphthol yellow, Violet 4B, and 
Cyanol, but viewed by gaslight the shades are quite different. 
The addition of a crimson dye to the indigo may convert it 
into a bluish-black, while the same addition to the mixture 
may produce reddish-black. These differences in effect are 
due to differences in the absorptive action of the colouring 



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COLOUE PHENOMENA AND THEOEIES. 71 

matters on the light — the eye, as it were, sees the mean of the 
rays of Kght which are transmitted or reflected, but it has no 
power of distinguishing what particular groups of rays are 
actually present, yet the character of the shades which may 
be produced by the admixture of various dye-stuffs together 
always depends upon the character of the rays which those 
dye-stuffs transmit or reflect, and not upon what is seen by 
the eye. It may be broadly stated that when dye-stufl*s whose 
absorption spectra more or less overlap one another are mixed, 
then it is the overlapping portion which governs the shades 
which are produced. The larger this portion is, the brighter 
and more luminous will be the hue of the colour visible to the 
eye ; the smaller the overlapping portions are the less luminous 
and duller will appear the shades. When dye-stuffs are used 
whose spectra do not overlap one another, then black will 
invariably ensue. 

We may now devote some attention to the subject of 
primary and c omple nientary colours. It has already bben 
pointed out that the painter being able, using red, blue and 
yellow pigments, to produce all colour effects, led to the 
development of the Brewsterian theory of there being three 
primary colours — red, yellow and blue. This theory having 
a good many practical applications we will devote some atten- 
tion to it. By the combination of .two of these primary 
colours we get, as described, a series of three other colours, 
which are known as secondary colours, these being orange, 
green and violet — the orange from the combination of the red 
and yellow; the green from the combination of the yellow and 
blue ; and the purple or violet from a combination of the red 
and blue. Then by the combination of these secondary 
colours .together in pairs or with a primary colour, we get a 
series of other colours which are called tertiary colours. 
Coloured diagrams on Plate IV., and also Figs. 49 and 50, illus- 
trate this theory of primary, secondary and tertiary coloura 



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72 THE THEORY OF COLOUR. 

The diagrams take the form of triangles, the sides of which 
are filled with a primary or secondary colour overlapping at 
the corners ; the central portion is also filled with a colour, 
which is produced by the union of the three colours forming 
the plate. In the triangle in Fig. 49 are employed the three 
primary colours — at the top red, left-hand side yellow, and the 
right-hand side blue ; the red and yellow overlapping at the 
top left-hand comer form the secondary colour orange, similarly 




Fig. 49. 

the red and blue overlapping in the top right-hand comer 
form the secondary colour violet, and the blue and yellow 
where they overlap at the bottom corner form green, while 
in the middle is a tertiaiy colour formed by the union of the 
three primary colours formed in constructing this diagram. In 
Fig. 50 we have the triangle formed from the three secondary 
colours ; at the left-hand side is green, right-hand side violet, 
and at the bottom orange; where the green and the violet 
overlap at the top corner we have the tertiary colour com- 
monly named slate ; at the left-hand bottom corner we have 



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COLOUK PHENOMENA AND THEOBIES. 73 

the green and orange overlapping when we get the tertiary 
colour named citrine ; while at the right-hand bottom comer 
w^ have the violet and green overlapping forming the tertiary 
colour usually named russet. In the centre is a more complex 
colour formed by the union of the three secondary colours. 
The diagrams (Figs. 49 and 50) should be compared with the 
corresponding coloured diagra^ns on Plate IV. The combination 
between tlie primary and secondary colours to form the tertiary 




Fig. 50. 
Fig. 50. 

colours may take place in a great variety of ways, and con- 
sequently there can be produced a large number of shades of 
tertiary colours depending upon the relative proportions of 
the constituent colours from which they are formed. 

The tone, tint, or shade of a colour are terms which are 
frequently met with in colour work, but they are somewhat 
indefinite, and are used by colourists rather indiscriminately. 
If a colour is mixed with a white pigment we weaken or re- 
duce its tone ; by using various proportions of the two (the 
colour and the white) we get quite a range of colours, these 



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74 THE THEOBY OF COLOUR. 

are known as tints. By mixing black with the pigment we 
render it duller and produce shades as they are called. Thus 
we may have quite a scale or range of shades according to the 
relative proportions of the black and the pigment; we can 
therefore distinguish between tints and shades. 

First, we have a reduced scale of tints made by mixing the 
colour with white. 

And second, a darkened scale of shades which fl,re produced 
by mixing the colour with black. 

The tertiary colours are always more or less dull, this is to 
be accounted for by the fact that a mixture of the three 
primary colours should produce black, but in the tertiary 
colours one or other of these three primary colours predominates, 
and it is this predominating colour which produces the hue of 
the tertiary colour. 

It has been found that, in mixing the primary colours, the 
best effects are not obtained by mixing the pigments employed 
in equal weights, but rather in what may be called equivalent 
proportions : thus, it has been found that three parts of yellow- 
require five parts of red to make a good orange ; in the same 
way it has been found that three parts of yellow require eight 
parts of blue to form a green, and that eight parts of blue are 
able to combine with five parts of red to form a violet. These 
numbers three, five and eight are considered to be the equiva- 
lents of yellow, red and blue respectively; but too much stress 
must not be laid on these colour equivalents, for they vary 
with the particular pigments which may be used; however,, 
they will occasionally serve a convenient purpose. By pro- 
portioning the red and yellow, yellow and blue, or blue and 
red, we can produce a variety of tints of the secondary colours : 
these we may represent in the following manner, using the 
letters R, Y and B for the three primary colours : — 



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COLOUE PHENOMENA AND THEORIES. 75^ 

; Y + R = Orange. 

2Y + R = Yellowish-orange. 
Y + 2R = Reddish-orange. 
; R + B = Violet. 

2R + B = Reddish-violet. 
R + 2B = Bluish-violet. 
B + Y = Green. 
2B + Y = Bluish-green. 
B -I- 2Y = Yellowish- green. 



COMPLEMENTARY COLOURS, 

It has been shown that when two coloured lights are 
mixed together white light is produced. This statement is 
only true of certain combinations, such as blue and yellow, 
and green and purple (see page 65) ; such pairs of colours are 
said to be complementary to one another. We find that a 
knowledge of pairs of complementary colours is of consider- 
able importance from the artistic point of view, inasmuch as 
the colours thus paired appear of the greatest possible con- 
trast to one another, while at the same time they harmonise 
more together than any other combinations — as, for instance, 
a red design on a green ground shows up much more distinctly 
and harmonises better than a red on blue or a red ton violet. 
Similarly a yellow design on a blue ground shows up much 
more strongly than a yellow design on a green ground. 

All the spectrum colours are primary, and each of them 
has its own particular complementary colour situated in some 
other portion of the spectrum. We may give here a table of 
the complementary colours of the principal divisions of the 
spectrum : — 

TABLE OF COMPLEMENTARY COLOURS. 

Red Bluish-green. 

Orange Deep-blue. 

Yellow Ultramarine blue. 

Greenish-yellow Violet. 

Green Reddish-violet. 



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76 THE THEOBY OF COLOUR. 

Many other pairs could be formed. The colours which lie 
between the red and the orange have their complementary 
colours between the bluish-green and cyan blue. The colours 
which lie between yellow and green find their complementary 
colours in the portion lying between the ultra-marine blue and 
the reddish-violet. 

The best plan of studying the production of complementary 
colours is by means of the polariscope arranged in connection 
with selenite plates of varying thickness, to, produce discs of 
colour such as those shown in Figa 5 to 8 on Plate III. It is 
the best way of producing complementary colours, and gives 
by far the most' satisfactory results. It is impossible in words 
to convey an idea of the exact shades of the pairs of colours 
which are complementary to one another. It is not always 
easy to piatch them by painting, but it is only in this way that 
a meaning can be conveyed. • 

The polariscope does not, however, give us the comple- 
mentary colours of many tints which can be produced by 
pigments and of which it is desired sometimes to know the 
complementary colours. This is especially the case with 
olive-greon, brown, and other shades of a similar character. This 
is due to the fact that the colours, obtained by the polariscope 
in conjunction with selenite, are very largely diluted with 
white light, which considerably increases their luminosity, 
whereas the colours referred to have a very weak luminosity. 
We can, however, obtain a solution of this proble!fei by means 
of the Maxwell discs, by taking advantage of the fact that the 
rotation of two primary colours tpnds to produce a grey ; if 
we take the colour which we require to match, and employ 
other discs, arranged so that with 'other primary colours they 
will produce a grey. Such a combination is shown in Fig. 51, 
where we have a combination of three large discs — a red, a 
green, and a blue ; and two small discs — one black and one 
white. The black and white when rotated give the sensation 



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COLOUB PHENOMENA AND THEOEIES. 



77 



of grey. Red is the colour which it is desired to match, then 
by mixing green and blue in certain proportions and rotating 
the discs we get a grey matching that of the central discs ; 
the colour produced by combining green and blue is therefore 
conaplenientary to the red. Again, Fig. 52 shows the manner 
of producing a complementary colour to a yellow ochre ; the 
yellow required more blue than green to obtain a grey identical 
to that produced by the rotation of the black and white discs. 




Fig. 61. 

Even this method is not altogether satisfactory, for the relative 
intensities and luminosities of the pigments used in the pro- 
duction of the discs have a considerable influence in modifying 
the results. It is only possible to obtain the true complement 
of a colour by combining it with other colours having 
equal degrees of intensity and luminosity Unfortunately 
this is rarely the case, as the red and yellow pigments — car- 
mine, vermilion, chrome yellow — are much more luminous 
than the green and blue pigments — emerald green, cobalt blue,. 



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78 



THE THBOKY OF COLOUR. 



ultramarine — which can be employed in this method of pro- 
ducing complementary colours. 

In painting, and also according to the Brewsterian theory 
of colour, the term complementary is employed in another 
sense. According to the theory there are three primary- 
colours — red, blue and yellow. Now by mixing these three 
together we get three other colours, orange from the yellow 
and red, green from the yellow and blue, and purple or violet 




Fig. 52. 

from the red and the blue. These are called secondary colours, 
and each secondary colour is considered to be complementary 
to the primary colour which is not used in its production ; 
thus, green is regarded as complementary to red, blue to 
orange, yellow to violet. This is illustrated in the coloured 
chart Fig. 5, Plate IV., which depicts a triangle each side of 
which is occupied by a primary colour, while at the tips the 
colours overlap to form the secondary colours. The primary 
on one side is complementary to the secondary in the corner 
opposite to it. The coloured triangle No. 6, Plate IV., shows 



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COLOUR PHENOMENA AND THEORIES, 79 . 

in a similar way the secondary colours, orange, green, and 
violet, and at the comers the tertiary colours formed from them, 
each of the latter being complementary to the secondary facing 
it, slate to orange, citron to violet, russet to green. 

SUPPLEMENTARY COLOURS. 

This is a term used in some text-books to indicate the colour 
^which is left when two of the primary colours are taken from 
any combination. It is, however, a term which is extremely 
vague in its derivation and use. 

Colour Theories. — Having discussed at length the pheno- 
mena of colour production and admixture it will now be con- 
venient to consider some of the theories which have been 
propounded from time to time to account for these phenomena. 

Brewster's Theory. — This theory has several times been 
referred to in connection with primary and secondary colours, 
and its bearings have already been adequately discussed. 
The red, blue, and yellow primary theory fails, however, to 
account for all the colour phenomena which can be produced, 
chiefly because it was not based on an examination of the 
composition of coloured lights. 

Young- Helmholtz Theory. — Thomas Young was the first 
to point out that Brewster's theory did not explain the re- 
sults which can be obtained by mixing the spectral colours 
together, nor the effects which can be got by means of the 
revolving Maxwell discs. He therefore propounded the 
theory of three primary colours consisting of red , green and 
bluej__this theory, more fully developed by Helmholtz, is 
known as the Young-Helmholtz theory, and, seeing that it 
explains in a fairly satisfactory manner all colour phenomena, 
it has become almost universally accepted as being correct. 

According to this theory the three primary colours are 
red, green and blue. Now as there are various hues of 



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80 THE THEOKY OF COLOUR. 

these colours, some difference of opinion naturally exists 
amongst colourists as to the exact hue which should be 
adopted as a true primary colour, particularly as regards 
the blue. The primary red is usually accepted to be one 
having about the same hue as carmine or a mixture of equal 
proportion, of carmine and vermilion, the green resembling 
emerald-green in hue, being perhaps a little deeper in tone, 
the blue approaching the tone of Prussian blue. Some 
colourists are inclined to regard the true primary blue as 
being a little greener in tone than Prussian blue, while others. 
Maxwell and Miiller, consider the primary blue as one having 
a more violet hue, like ultramarine. 

When two of these primary colours are mixed together 
secondary colours are obtained; thus red and green yield 
yellow, green and blue give a greenish -blue, named sea green, 
while red and blue give a purple tint. It will, be noted that on 
mixing two of these colours we get the tint which occupies 
an intermediate position in the spectrum. When the three 
primary colours are mixed together we get white light. It 
is, however, necessary to point out that the results which are 
here stated to be obtained can only be got with spectrum colours 
or the colours obtained with the polariscope ; only an approxima- 
tion can be obtained with coloured lights thrown from several 
sources on a screen (see Plates No. II., Figs. 2 to 5, and No. III., 
Figs. 5 to 8). If three optical lanterns are arranged to form 
three overlapping discs on the screen, and in one there is a red 
glass, in the second a green glass, and in the third a blue glass, 
it will be found that where the red and green overlap yellow 
is obtained, where the red and blue overlap then violet is 
produced, and where the blue and green overlap a greenish- 
blue is the result, while in the centre will appear a triangular 
white space where all three of the colours overlap. 

To obtain the best results, care is necessary in selecting 
the red, blue and green glasses so that they may be of the 



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Plate vi. 




(Theory of Colour). 



Colour Contrasts. 



To face p, 80. 



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COLOUR PHENOMENA AND THEORIES. 81 

right hue, and probably many will have to be rejected before 
the right ones are obtained. 

We now see the fundamental difference between the old 
and the new theories. In the old theory, based upon the ad- 
mixture of pigments, the admixture of the three primary 
colours gives rise to the production of a tertiary colour ; while 
in the newer theory white is the result, which is not only 
true in theory but in fact, for, as already explained, white 
light is composed of all the colours of the spectrum, and these 
are mutually complementary. 

If, instead of adding coloured lights together to form 
white light, we take away one of the primary colours from 
white light, there will be left, according to the Young-Helm- 
holtz theory, a combination of the other two primaries : thus, 
if we take away blue there will be left yellow, which is 
produced by the combination of the other primaries red and 
green; if the red be next taken away we shall have green 
left ; and if this be taken away we shall have no light at all ; 
in other words, all the rays of light are removed and black- 
ness results. Now it having been shown that the colour of 
bodies is due to their possessing an absorptive action on the 
light which passes into them, a black body is black because 
it absorbs all the light which enters into it. 

According to the Young-Helmholtz theory the colour effects 

obtained by mixing pigments, dyes or colouring matters 

together are due to the absorptive action of the colouring 

matters upon the light which falls upon them. This 

absorptive action results also in a reduction in the intensity 

of the light, therefore the colour which is produced by the 

mixture of two or three other colours is weaker as regards 

its light intensity and therefore appears duller or darker ; in 

the end, by total absorption of all the light, black results. 

How soon this o'ccurs depends entirely upon the colouring 

matters which are used ; in some caaes— as, for instiance, when 

6 



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82 THE THEOEY OF COLOUE. 

the dyer uses Azorubine and Acid Green — two will suffice, 
in other cases three or more may be required. 

If the colouring matters are so mixed together, that while 
there is considerable reduction in the intensity of the light, 
the colours being such as would form an orange — that is, 
red and yellow predominate — then brown will result ; if, on 
the other hand, green is predominant the resulting colour 
will have an olive hue, while plum shades will result when 
the red and blue predominate. 

In a similar manner we may account for the production 
of all the secondary and tertiary hues produced by the ad- 
mixture of pigments and colouring matters together. If 
there is an absorption of light which tends to produce the 
same effect as adding black, then the predominant colours 
show themselves somewhat in the manner indicated above. 

Maxwell's Theory. — This closely resembles that of Young 
and Helmholtz, differing from it only as to the hue of the 
primary colours. Maxwell regards scarlet, green and a 
violet tone of blue like ultramarine as the primary colours, 
the wave lengths corresponding to the true primaries being 
in millionths of an inch, for the scarlet 2328 between lines 
B and C, for the green 1914 near line E, and for the blue 
1717 near line G. As regards the secondary colours obtained 
on mixing the primaries together and the relationship of 
primary and complementary colours, Maxwell agrees in all 
essential particulars with Helmholtz. In 1861 Maxwell 
demonstrated the correctness of this theory in lectures at 
the Royal Institution. 

A solution of sulphocyanide of iron matches well the 
primary red, one of chloride of copper the primary ^een, 
and one of ammoniacal sulphate of copper the primary 
blue. With three lanterns, and using troughs filled with 
these solutions, many experiments on the mixture of the 
primary colours may be m^de. 



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COLOUR PHENOMENA AND THEORIES. 83 

Colour Photography. — The production of photographs in 
the colours of nature has occupied the attention of scientific 
men for a very long period, and, although it is not yet 
possible to produce a coloured picture at one operation on 
paper by photographic means alone, the results obtained 
with transparencies and by the aid of the three-colour 
process of printing are very beautiful and fully repay for 
the labour already spent, at the same time giving promise 
of further developments in the future. 

In the early days of photography the attempts necessarily 
lacked any scientific basis, but since the theories of Young and 
Helmholtz and Clerk Maxwell were propounded the subject 
has developed on a firmer footing and much more rapidly. 
The phenomena underlying colour photography are therefore 
the same as those described in this book which renders it an 
interesting subject for us to study from this point of view. 

Several of the early experimenters in photography appear 
to have produced coloured pictures on paper sensitised with 
silver salts, although they were not able to fix them and 
render them permanent. Thus in 1839 Sir John Herschel, 
at a meeting of the Royal Society, described the production of 
a coloured image of the spectrum in this way. Whether the 
colours were as brilliant and true in position as those of the 
spectrum or were simply due to iridescence we do not know, 
but the existence of coloured haloid salts of silver was de- 
monstrated in 1887 by W. Carey Lea, who named them 
" photo-salts," these being produced from the chloride, bromide, 
and iodide of silver by reducing agents and also by the action 
of light. 

The first step of any importance in colour photography was 
made by Professor Clerk Maxwell, who, lecturing at the Royal 
Institution in 1861, exhibited a number of interesting experi- 
ments on light and colours. He showed among other things 
three photographs which had been taken of the same coloured 



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84 THE THEORY OF COLOUR. 

object under a red, blue, and green glass respectively. On 
projecting these together from three optical lanterns, each* 
photograph being illuminated by the light with which it 
was taken, an image was obtained which showed the colours 
of the original 

In 1865 Henry CuUen described how it might be possible 
to obtain a coloured photograph taking three negatives of 
the same object, one under a blue, one under a red, and one 
under a yellow screen, then by using these in pairs, and ex- 
posing over a film which was sensitive only to the remaining 
colour three positives would be obtained which when laid 
upon one another on a white surface would give the form 
and colours of the original object. Although merely theo- 
retical at the time thess ideas were later carried out. In 
1867 Charles du Cros obtained a patent for a process in whidh 
three negatives were prepared, the subject being illuminated 
with red, yellow, and blue light in rotation. Positives were 
made from these negatives, then stained, and on examina- 
tion in a suitable apparatus they were combined to form 
one multicoloured image. A year later Duces du Hauron 
brought forward two processes, one of which introduced a 
new principle, that is the use of a screen ruled with lines 
of three colours, later elaborated by Joly. In 1869 Ducoa du 
Hauron introduced another process, using screens as above, 
but printing upon separate transparent films tinted with the 
complementary colours, the three being combined. In 1881 
Du Cros described still another method in which a sensitive 
surface was tinted with certain colours each of which was 
bleached when exposed to light the colour of which was 
complementary to it. 

Mr. F. E. Ives, of Philadelphia, considerably improved upon 
anything which had been done before by applying the results 
of Clerk Maxwell scientifically, and introduced three colour 
screens which were adapted to give accurately the three colour 



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COLOUE PHENOMENA AND THEOBIES. 85 

sensations as shown in Fig. 58. In this process a special 
camera capable of taking the three pictures at the same time 
is employed. The times of development have to be adjusted 
so as to obtain as nearly as possible equal density on all the 
plates. Then by examination of the three together in an in- 
strument called the " Photochromoscope " or **Kromscop" a 
perfect coloured picture was obtained. 

The Photochromoscope consists essentially of a box, open 
at both ends, with three coloured glasses or screens (red, green 
and blue-violet) and three pairs of small mirrors arranged 
within it. With such a simple device it is possible to view the 
monochromatic triple image of the chromogram as a single 
image reproducing all the colours of the object photographed ; 
but in order to magnify the image, to improve the illumination, 
and in other respects to add to the efficiency and convenience 
of the instrument, it is constructed upon a more elaborate plan, 
with condensing lenses, colour screens, mirrors, objective lens, 
focussing eye-piece, etc. 

THE KROMSKOP. 

This instrument consists of a case with five pieces of 
coloured glass, a reflector and eye-lenses, which are so disposed 
as to blend the images, either single or stereoscopic, and focus 
them upon the retina. 

The construction and operation of the Kromskop may be 
readily understood by reference to a diagram (Fig. 53). A, B 
and C are red, blue and .green glasses, against which the cor- 
responding images of the negatives are placed when the in- 
strument is in use. 

D and E are transparent reflectors of coloured glass. F 
represents the eye-lenses for magnifying the image. Beyond 
C is a reflector ; for illuminating the images at C, those at A 
and B being illuminated by direct light from above. 

The operation of the Kromskop is as follows : The green 



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86 THE THEOBY OF COLOUB. 

image is seen directly, in its position at C, through the trans- 
parent glasses D and E. The blue image is seen hy reflection 
from the surface of the glass, D, and also appears to form part 
of the image at C. In the same way the red image is seen by 
reflection from the surface of the glass, E, and also appears to 
form part of the image at C. And flnally the eye-lenses at F not 
only magnify but cause the eyes to blend the two images which 
constitute the complete stereoscopic pair, as in the ordinary 
stereoscope. The result is a single image, in solid relief and in 
the natural colours. 




More recently a similar although simpler instrument was 
invented by Barnard and Gowenlock to which the name 
** Elromaz " was applied. 

In 1895 Professor J. Joly of Dublin described his process 
in which only one negative is needed, this being taken through 
a screen ruled with extremely fine lines in red, green, and 
blue-violet alternately, which is placed in intimate contact 
with the negative. The plate used is a panchromatic one, 
that is, sensitive to all colours, and a yellow screen is also 
employed to cut down the blue and violet rays which are 
photographicajly ^ much more active than the others. The 



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COLOUB PHENOMENA AND THEOBIES. 87 

effect on the negative is to produce a number of fine lines 
corresponding to the different colours acting, and in their 
proper place on the negative. By viewing a positive made 
from the above negative through a similarly ruled screen in 
which appropriately coloured lines are ruled, the objects ap- 
pear in their proper colours. 

In the Sanger Shepherd process three negatives are taken, 
either at one and the same time in a special camera, or sepa- 
rately in an ordinary camera, through red, green, and violet 
filters, the times of exposure necessary to obtain equal density 
on the three negatives being regulated by a preliminary trial. 
From the negative taken through the red filter a greenish- 
blue print is obtained by making from it a black tone lantern 
plate, bleaching this in a solution of ferricyanide of potassium 
and then staining in a greenish-blue (or minus red) medium 
and fixing in hypo. The pink (or minus green) and yellow 
(or minus blue) films are made upon a sensitised celluloid film 
from the other two negatives. This film contains gelatine and 
bichromate of potash, so that after exposure the portions 
unacted upon by light can be removed by warm water. The 
bromide of silver is then removed from the picture by im- 
mersion in hypo. The prints now appear quite clear. They 
are cut up and steeped in the appropriate dyes, forming the 
pink and yellow images. 

The pink film is now placed over the greenish-blue lantern 
plate and upon this is laid the yellow film, the whole being 
moved about until they appear in proper register, they are 
then bound together and the picture is complete. The trans- 
parencies thus produced can be shown with the optical lantern 
or in a stereoscope, the results being exceptionally good. 

MM. Auguste and Louis Lumifere of Lyons have intro- 
duced two methods of colour photography, the original con- 
sisting in taking three negatives through green-blue, violet 
and orange screens respectively. From th«e negatives three 



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88 THE THEOBY OF COLOUB. 

prints are obtained on bichromated gelatine papers, the prints 
being developed in warm water and then stained by suitable 
dyes; that taken from the negative exposed to green light 
being dyed red ; that from the blue- violet negative, yellow ; 
and that from the orange negative, blue. After stripping 
these from their paper supports the gelatine films are super- 
imposed and fixed in proper position upon one support. 

The later Lumifere process is, however, of more interest, as 
it introduces an ingenious method whereby only one negative 
is required. The negative is prepared by spreading upon 
glass a mixture of fine starch granules having a diameter of 
tijtjVtt ^ aoooo of a millimetre, these being stained in three 
colours, ried-orange, green and violet. The starch grains are 
fixed in position by a varnish and upon- this is poured a 
panchromatic emulsion — that is one sensitive to all colours. 
The plate is exposed in the camera with the glass side towards 
the lens, so that the light passes through the coloured starch 
grains before reaching the film. Each starch grain thus acts 
as a light filter for its particular colour, and a negative is 
- obtained covered with minute dots representing colour im- 
pressions. From this negative a positive plate is prepared 
which when viewed in conjunction with a similar screen to 
that used in taking will give a coloured image. 

The diffraction grating process due to Professor R. W. 
Wood of Madison, U.S.A., is another ingenious method of colour 
photography. Three negatives are here required, made from 
the same picture, using screens of red, green, and blue- violet. 
These negatives are then exposed in rotation over a single 
positive plate, sensitised with bichromated gelatine, but with 
each negative a diffraction grating is also employed. The 
diffraction grating for red having 2000 lines ruled to the inch, 
that with green 2400, and that with violet 2700. The positive 
is then developed by soaking in warm water which dissolves 
out the unaltered gelatine. Viewed in the ordinary way, this 



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r iv/v 1 r.. V 11. 



A.— Yellow Print. 



C. — Combination of Yellow and Red 




Coniljined Three-Coloirr 1 



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'nut. O 



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COLOUR PHENOMENA AND THEORIES. 89 

positive shows practically nothing, but when viewed in a 
special apparatus and illuminated by light passed through a 
lens the objects in their natural colours become visible. 

The Paget process of colour photography has certain 
features which recommend it for general use. It is simple 
and inexpensive, while the negative may be used for ordinary 
printing out as well as colour printing, at the same time any 
number of coloured positives can be obtained from it. The 
negative is taken in an ordinary camera behind a taking 
screen which is covered with a regular pattern of minute 
squares of red, blue, and green. A yellow light filter is also 
employed to reduce the effect of the blue and violet rays. 
The negative does not differ in appearance from an ordinary 
negative. From this negative a transparent positive is made 
in the ordinary way. The positive is then placed under a 
viewing screen, similar to the taking screen, and the two 
moved about into register, when the colours appear exactly as 
in the original subject; the two are then bound together. 

An interesting development of colour photography is the 
three-colour process of printing. In this method the negatives 
are prepared as already described, using red, blue, and yellow 
screens respectively. It must be remembered that these 
screens not only allow the particular pure colour to pass 
through but also that portion of the same colour which is 
present in secondary and tertiary tints. Thus blue allows 
pure blue to pass and also a proportion of the green, yellow 
allows yellow to pass and also orange, while red allows red 
to pass and also a portion of the violet. From these negatives 
positives are prepared on zinc blocks sensitised on the surface 
with bichromated gelatine. These are developed in the ordin- 
ary way and after further treatment are etched with acid, the 
particular coloured portions standing in relief. The picture is 
printed with these blocks in rotation using the proper coloured 
inks, the result being a picture which is remarkably natural 



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90 THE THEOBY OF COLOUR. 

in its appearance (see Plate VII.), and a great step in advance 
of the old-fashioned coloured pictures in which a separate 
block had to be used for every colour, simple or compound, 
and which therefore was limited to a very few tints, which 
did not blend with one another but stood out in bold relief, 
thus giving a very harsh and unnatural effect 

The foregoing outline of the development of colour photo- 
graphy, although necessarily limited in its scope, serves to 
show the value of the practical application . of the colour 
theories which have been described in this book. 

Hering's Theory. Bering has proposed a theory in which 
it is supposed that there are six primary colours, arranged in 
pairs, black and white, red and green, and blue and yellow, 
each pair being connected with corresponding sets of nerves in 
the eye, but this theory does not add anything to our know- 
ledge of colour vision. The physiological aspect of the various 
colour theories will be discussed in the chapter on the 
physiology of light. 



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CHAPTER IV. 
THE PHYSIOLOGY OP LIGHT. 



The sense organ by means of which we perceive the pheno- 
mena of light and colour is the eye. of which man has two, 
situated in the upper portion of the face, and each similarly 
situated. The eye is a globe loosely placed in a cavity known 
as the orbit, its movements being controlled by a number of 
muscles ; the eye and the orbit are shown in Fig. 54. A 
section of the eye is given in Fig. 55, where it is seen to be a 
hollow ball formed of a very dense 
and muscular tissue, the front por- 
tion of which is transparent, while 
by far the largest portion is opaque. 
The transparent portion is known 
as the cornea, shown at Cn in 
the figure. The opaque portion is 
called the sclerotic, and is shown 
in the figure at Scl. The interior 
is divided into two cavities, a small 
anterior cavity at Aq next to the cornea, and a posterior cavity, 
Vty by means of a transparent crystal structure Cry, the 
fimction of which is to act as a lens on the light which passes 
through the cornea. In front of the lens is a kind of diaphragm, 
7r, known as the iris, in the centre of which is a circular hole, 
the pupil, the main use of which is to simply allow the light to 
pass through the central portion, which is the most useful portion 
of the lens. The anterior cavity, Aq, is filled with what is known 

(91) 




ER. 



Fig. 54. 



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92 THE THEOBY OF COLOUB. 

as the aqueous humour, while the posterior cavity is filled with 
a fluid substance known as the vitreous humour. In dose con- 
tact with the sclerotic is a muscular member which, on account 
of its containing polygonal cells and pigmentary matter, is 
known as the choroid, marked Ch in the drawing ; this choroid 
coat goes all round the interior of the eye, and in front it is 
attached to the muscles of the lens by ciliary processes. 
Immediately in front of this coat is another highly important 




one, the retina, marked Rt in the drawing. This retina is a 
highly nervous structure, which plays an important part in the 
observation of light. The retina is in connection with the 
optic nerve and is a continuation thereof, as is shown in the 
drawing where Op represents the optic nerve. 

Fig. 56 is a vertical section of the human retina as seen 
under the microscope. There is first of all at i next to the 
sclerotic what is known as the anterior limiting membrane, 
while next to this is a layer of nerve fibres which separate 
themselves up into the small fibres, passing through the sub- 



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THE PHYSIOLOGY OF LIGHT. 



93 



stance of the retina. Upon this at hH is a layer of nerve 
• cells ; again above these is a mass of granular tissue, the 
granular layer as it is called, and a small layer is at gg\ while 
between these two occurs what is known as the anterior 
nuclear layer^ a small layer ; the exterior layer is at dd\ At 
6c is what is known as the external 
limiting membrane, which allows the 
nerve fibres to pass through to the un- 
dermost portion of the retina. This 
consists of a layer, 6, of rods and cones 
as they are called. It is in this layer of 
rods or cones that the nerve sense for 
light is supposed to reside. The retina 
is uniformly distributed over the surface 
of the eye except at two places, one in 
the middle and in the line of vision, 
where there is a slight depression of a 
yellowish hue, this is known as the 
" yellow spot," or the macula lutea, and 
the blind spot, which on the under side 
has a radial appearance, caused by the 
entrance of the optic nerve, which 
spreads over the retina from that point 
as a centre. 

At the yellow spot the rods are ab- 
sent, ^nd the fibres fewer in number, only the cones being 
present, while the yellow colour is due to a small deposit of 
pigmentary matter. 

Persistence of Vision. — When an image of an object is 
formed upon the retina it remains there for a perceptible 
period of time. This duration of the impression on the retina 
is the cause of many illusive phenomena being observed by 
the eye. Thus if a black disc be fitted to the rotatory appa- 
ratus shown in Fig. 44, and on this disc is placed a small 




Fig. 56. 



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94 THE THEOEY OF COLOUR. 

patch of white, the disc then being rotated, we observe, not a 
patch of white on black, but a grey ring which does not vary 
in intensity with rapidity of rotation. The tint of the grey 
produced depends upon the proportion between the patch of 
white and the amount of black at the particular distance from 
the centre of the disc ; if the white patch be made longer then 
the grey will be lighter, but if the patch be shorter then it 
will be darker. If a disc be so arranged that one half of it is 
black, and the other half white, then the grey which is 
produced by the rotation of the disc has half the luminosity 
of white light. That this is so can be proved experimentally 
in the following manner: A prism of calcspar will produce 
two images of a strip of white paper ; each of these images is 
just one half or nearly one half the luminosity of the original. 
Now if the grey produced by the rotation of the black and 
white disc be compared as regards luminosity with one of the 
images formed by the calcspar, they will be seen to be 
practically the same. 

Grey may be produced by the rotation of a disc which 
<;ontains alternate black and white spots. The intensity of 
the grey is not changed by an alteration in the speed of rota- 
tion and it is quite independent of the absolute duration of the 
periods of light and dark. This can be shown by the employ- 
ment of the disc shown in Fig. 57, in which the disposition of 
the black and white portions is such as to produce variations 
in the proportions or duration of light and dark as the disc 
rotates. If this disc be rotated at a speed of twenty revolu- 
tions per second, then the periods in which these alternations 
of light and dark exist are, for the inner zone ^ of a second, 
in the middle zone ^ of a second, and in the outer zone ^ of 
a second, the alternations of light and dark being equal. On 
rotating the disc it will be noticed that the grey produced in 
the three zones is of the same degree of brilliancy, while a 
quicker speed of rotation makes no difference in the results. 



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THE PHYSIOLOGY OF LIGHT. 95 

Many fireworks, notably the pin wheej, depend for their 
brilliancy and form upon this phenomenon of persistence of 
vision ; they are produced by the rotation of a single point of 
light. Perhaps the simplest of such experiments is when a 
live spark on the end of a stick is made to revolve, when it 
produces a ring of light, and yet it is very evident that at any 
43ingle moment there must be just a minute spot of light and 
not a ring at all. In such a phenomenon the rapidity of 




Fig. 57. 
rotation is of importance; the motion may be so slow as not 
to show the presence of a ring of light at all ; there must be 
a certain degree of rapidity, and from observations made by 
D*Arcy the average rate of rotation should be one revolution 
i^ TQo of a second, but the rapidity varies with different 
bodies. Thus in some cases it is necessary to have a re- 
volution once in /g of a second. This is the measure of the 
duration of an impression produced on the retina with almost 
full intensity, but there is reason for thinking that the dura- 
tion is often less than this, then it decreases and fades away 



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SpeaKine 



96 A JfTHE THEOBY OF COLOUR 

entirely. Speaking generally the time of duration may be 
taken as J of a second. The spokes in a revolving wheel are 
separately invisible from the same cause, the position they 
occupy taking the form of a nebulous disc. 

This persistence of vision gives rise to various colour 
phenomena of a rather uncertain character, some of which 
are fairly familiar to many persons. If, for instance, a piece 
of red paper is hung against a white wall and observed fixedly 
for a few minutes, and then the eyes riveted upon another 
portion of the white wall, a faint green image resembling that 
of the red paper is observable. If a piece of yellow paper be 
substituted the after-image will have a bluish tint. The first 
impression, of the red or yellow paper in the above experi- 
ments, produced on the retina is called the positive image; 
while the spectral image, which is of a. fainter character, is 
the negative image or after-image. Another method of carry- 
ing out -this experiment is to take a sheet of grey paper, 
place it on a piece of green paper, and look at the latter 
attentively for several seconds; then suddenly remove the 
green paper, when its place is taken by a rose-red image, 
which, however, disappears very shortly. If in place of the 
green paper, red is used, then the image will have a greenish- 
blue 'colour. In the same way blue gives rise to a yellow 
image, violet to greenish-yellow, orange to a blue, the colour 
of the image being in all cases the complementary of the 
original colour. ^ 

We can explain these colour phenomena according to the 
theory of Young and Helmholtz in the following manner : In 
the eye there are three sets of nerve fibres, one set sensitive to 
green light, another sensitive to red, and a third sensitive to 
violet or blue light ; the grey paper has an equal influence on all 
the three sets of nerves. When we look at the green paper the 
nerves sensitive to green become fatigued and rendered inert ; 
on the other hand, the nerves sensative to red and violet 



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\ 



Plate VIII. 




(Theory of Colour). 



Colour Contrasts. 



Tf fac$ p. 96. 



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u._ 



-^^ 




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THE PHYSJO^d'CfY OVWXmV^^^^^ 97 

are not much affectedj Wherytne green paper is taken away 
then grey light is m4sented ij these fatigued nerves, which 
only faintly responl, while ojy the other hand the nerves sen- 
sitive to red and liolet re^ond considerably, between them 
a sensation of a mixture of red and violet, that of a rose-red 
image, is obtained. The nerves sensitive to green being 
fatigued affects this image so as to make it appear fainter. 

Again, take the effect which is produced when a piece of 
green paper placed on a yellow ground is suddenly removed, 
and we have an orange-coloured image of the green paper pro^ 
duced. This may be accounted for in this way : The green 
nerves are fatigued while the red and the violet nerves are still 
fresh ; when the green paper is removed, yellow light is only 
presented to the eye, and yellow being produced by a combina- 
tion of red and green, it tends to act upon the red and the 
green nerves equally, but the green nerves being already 
fatigued, do not readily respond, and so the red nerves oveis 
power the much weaker green nerves, the union of the red 
sensation and the yellow sensation on the paper gives rise to 
the effect of orange ; in this particular instance the violet rays 
are but little affected. 

If a small piece of black paper be placed upon a sheet of 
red paper and the patch of black observed intently for some 
time, on suddenly removing the latter, there will be observed 
a luminous spot of red, much more intense than that of the 
red ground. In a similar way, if a green ground be substituted 
for the red the after-image of the central spot is much more in- 
tensely green. We may explain these effects by considering 
that where the black spot is focussed upon the retina the 
nerves in that part are not affected to any appreciable extent 
— at all events the three sets of colour nerves would be equally 
affected ; but the red or green nerves, as the case may be, on the 
other portions of the retina being more or less fatigued, this 
fatigue causes a reduction in the intensity of the sensation they 

7 



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98 THE THEOKY OF COLOUE. 

produce ; while on the other hand, where the black spot has 
been, the red or green nerves are quite fresh, and readily pro- 
duce the appearance of a more intense image than the rest of 
the ground. 

This experiment also serves to illustrate another pheno- 
menon which is very frequently met with, and that is, when a 
coloured object has been looked at for some time, or when a 
number of objects of the same general colour, such as reds or 
greens, have been under observation for a long period, the eye 
loses it sensitiveness, the colours of the objects becoming dull, 
and losing their brilliancy. This may be explained by the fact 
that the coloured light from any coloured object not being 
quite pure, while in the main it acts upon one set of nerves, 
the other two sets are also brought into action to some extent • 
thus red light excites to a considerable degree the red nerves — 
it also excites slightly the green nerves and the violet nerves. 
The red nerves soon begin to be fatigued and lose much of 
their power, while the other sets of nerves are but slightly 
affected, therefore gradually the sensations of green and violet 
are added on to the red, and so the colour become's more greyish 
or of a dull tone. In the same way, while green excites most 
powerfully the green nerves, yet the red and the violet are also 
slightly affected ; the green soon loses its power, and the red 
and the violet begin to exert their influence and a greyish- 
green is the result. 

Clerk Maxwell having investigated the sensitiveness of the 
colour-nerves of the eye, has shown that, while the red colour 
nerves are most excited by red rays, they are also excited in 
a much lesser degree by other colours ; in the same way the 
green colour-nerves are most sensitive to green, but are also 
sensitive to other colours ; and similarly the blue colour-nerves 
are most sensitive to blue, still other colours excited them to a 
lesser degree. Fig. 58 shows the curves of sensibility which 
Maxwell has drawn for each of the three sets of colour-nerves. 



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THE PHYSIOLOGY OF LIGHT. 



99 



Dyers, calico printers and cloth examiners, who have to 
examine and pass coloured goods, find their judgment affected 
when they have been looking over a number of pieces of the 
same colour, the later pieces not appearing so bright or of the 



A B 




Fig. 68. 

same tone as the earlier pieces. To overcome this defect it is 
necessary to pass from one range of coloured goods to another 
range — as, for instance, from reds to greens or blues. 

This peculiar phenomenon is rendered more distinct if in 
place of the patch of black on a coloured ground we employ a 





Fig. 69. 

patch of a colour complementary to that of the ground — as, 
for instance, a patch of green on a red ground, or a patch of 
red on a green ground. When the patches are removed the 
subsequent after-images are much more intense, because they 
are surrounded by a colour having an entirely opposite effect. 



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100 



THE THEOBY OF COLOUE. 



Many examples of such colour phenomena might be given, 
but these are suflScient to illustrate what are commonly known 
as " successive contrast '* ; when we look upon twp diflerent 
colours in succession to one another. Persons who have, in the 
course of their business, to examine tints of coloured bodies, 
find this phenomenon of successive contrast to have a material 
influence upon the degree of perception of colour shades and 
tints. 

The eye is not a perfect optical instrument ; thus it is sub- 
ject to the phenomenon known as irradiation, and also to errors 
from imperfect judgment as to size, direction and relative 




Fig. 60. 



Fig. 61. 



distances or direction of objects ; thus in Fig. 59 we have a 
black spot on a white ground, and a white spot on a black 
ground— the two spots are identical in size, but according to. 
the eye the white spot appears to be larger than the black 
spot. In Fig. 60 we have another example of this, where a 
square is divided into four equal squares, two white and two 
black; on looking at these from a distance the white squares 
appear to be larger than the black squares, and further that 
they are joined together by a short strip of white, while, as a 
matter of fact, they touch each other at the points. Fig. 61, 
which is commonly known as ZoUner's lines, illustrates further 
that the eye is but imperfectly capable of judging correctly 



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THE PHTSIOLOGT OF LIGHT. 



101 



A\ 



\l/ 



V 



B 



/\ 



Fig. 62. 



The long diagonal lines, although parallel, do not appear to bB' 
so ; their inclination appears to differ. This effect is caused by 
the short lines which cross them — without these crossed lines 
the long lines would appear to be what they really are, i.e. par- 
allel. Then the judgment as to the actual length of a line is 
much influenced by the relationship 
of other lines; thus in Fig. 62 the 
two lines A and B are of the same 
length, although B appears to be much 
longer than A. Another instance of 
error of judgment as to size is in ob- 
serving a row of the letter S or a row 
of the figure 8 (see Fig. 63). Actually, 
the bottom halves of these figures are 
a trifle larger than the top halves, but 
to the majority of persons the top halves appear to be the same 
size as the bottom halves. 

We have seen above that, by bringing about the fatigue 
of certain sets of nerves, we can produce an image of an ob- 
ject of a different colour to that originally presented. These 
colours are sometimes known as subjective colours, and we 
can produce them in various ways. For instance, if a disc 

SSSSSSSSSS 

8888888888 
Fig. 63. 

of card is painted in alternate black and white sectors (or 
black painted upon a white ground), and placed upon the 
rotating machine — on rotating, the resulting disc will, after a 
short time, acquire a certain colour according to the speed of 
rotation ; thus a slow rate gives rise to the production of a 
green hue, while an increase in the rate of revolution changes 
it to a rose colour. Rood describes a method of observing 
these subjective colours by viewing the sky through a revolving 



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102 '' ' *j,^j, THEORY OF COLOUR. 

*dis(5 with Sectors;* with a slow rate of revolution the sky ap- 
peared of a red tint, with a higher rate of revolution a bluish- 
green tint was obtained in the centre, the outer portion being 
purple. The passage of a current or shock of electricity 
through the eye gives rise to the production of subjective 
colours, which vary with different persons ; while persons who 
have partaken of jsantonine see white objects in various colours, 
the violet end of the spectrum being invisible to them. 

Colour Blindness, — Many persons are deficient in colour 
sensations. This is independent of the fact that much con- 
fusion about colours results from the very defective nomen- 
dature which prevails. The defect referred to applies to an 
actual want of perception of certain colours ; for instance, a 
person may be unable to distinguish between a red and a 
green. This was the case with the eminent chemist John 
Dalton, to whom red of the most stating hue had the same 
appearance as a quiet greyish-green. Such persons are said to 
be colour blind, and the phenomenon itself is known as colour 
blindness, sometimes as Daltonism. To such persons the 
spectrum is restricted, they see in it only two or three colours. 
If they are deficient, as is usually the case, in the perception 
of the red rays, they only perceive two well-marked divisions, 
which they call yellow and blue, the yellow including all the 
spectrum lying between the extreme red and yellowish-green, 
while the blue includes the rest of the spectrum. Often there 
is in the middle portion of the spectrum a neutral » zone in 
which no colour is perceptible ; in the majority of cases this 
neutral zone is the position of neutral green to the normal 
eye. 

Maxwell, who investigated the phenomena of colour blind- 
ness with the aid of his discs, showed that any colour observed 
by those afflicted with this malady could be matched with the 
aid of two colours along with black and white, which proves 
that colour-blind people perceive only two of the three funda- 



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THE PHYSIOLOGY OF LIGHT. 103 

mental colours which are visible to the normal eye. Helmholtz 
has also investigated colour blindness, and arrived at the same 
results as Maxwell. The most commpn form of colour blind- 
ness is that one alluded to above, where the colour sensation 
representing red is deficient. In this case, red objects appear 
to be yellow, and it is not possible to distinguish between red 
and green. Another common form is where the eye is insensi- 
tive to the yellow — to such a person red and violet are easily 
distinguishable, but green and violet are confused together, 
as are also blue and red. Yellow has the same efiect as, and 
is indistinguishable from, a bright red; one portion of the 
spectrum is a neutral zone and appears of a grey tint. Again, 
although still more rarely, we meet with persons who are 
colour blind to violet. 

Of course there are degrees of colour blindness, as with 
other defects. In some persons the defect occurs only to a 
limited extent ; they may be able to distinguish the red from 
the green, but only with diflSculty, the difference not being so 
marked as with a normal-eyed person, while there are other 
cases where we get the extreme kind of defect, in which the 
person utterly, fails to distinguish between various colours. 
Persons who are colour blind have, of course, considerable 
diflSculty in matching colours — in fact, it is impossible for them 
to do* this correctly. One method of testing for colour blind- 
ness is to place before the suspected person samples of dyed 
cotton of various hues, and ask him to select those of the same 
kind ; if he mixes reds with greens and reds with yellows, it 
is evident that he must be deficient in colour sense. It may 
be remarked, in passing, that it is not suflScient to ask a person 
to' name the colour of a coloured object, and judge of the 
eflSciency of his colour vision thereby, for a person may, 
although not actually colour blind, give wrong names to 
the colours ; he must be asked to match one colour by means 
of another. 



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104 THE THEOEY OF COLOUB. 

Persons who are colour blind often confuse a colour that is 
a mixture of red and violet with a colour mixture of red and 
green ; hence colour blin.dness and the character of the defect 
may often be ascertained by placing before the colour-blind 
persons objects coloured with mixtures of red and green ; red 
and violet, and of green and violet, and asking them to match 
them by the aid of similar colours. A person colour blind to 
red will match a mixture of green and violet with red, while 
he would be unable to match a mixture of red and green, for 
to him this would give the sensation of white or grey. A 
person colour blind to green will match a mixture of red and 
violet with green, while a green or red also would show more 
or less white to him. The degree of perception of colour 
varies also with the same person at different periods of his 
life. This has often been noticed in the case of artists. The 
colouring of the great artist J. M. W. Turner changed con- 
siderably between hi« early pictures and his later ones, this 
change being usually ascribed to an alteration in the colour 
perceptive faculties of the artist. 

A normal-eyed person may actually render himself for a 
brief space colour blind, by looking intently for some time at 
a red or green surface, or looking through spectacles made of 
coloured glass. Having thus fatigued his eye to one of the 
fundamental coloured rays, he will be unable to distinguish ^ 
the colours of objects properly. Another plan which may be 
followed is to heat some soda in a Bunsen burner, when a 
yellow light will be obtained, sufficient to illuminate very well 
the whole of the objects in a room, although it is impossible to 
distinguish colours, red or green objects appearing to be quite 
black. Such facts as are thereby obtained serve to show how 
much colour adds to the beauty of objects. 



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CHAPTER V. 
CONTRAST. 

If we look at two coloured objects placed side by side it will 
l>e noticed that the sensation of colour or tone which each pro- 
vinces in our eyes is modified by the adjacent colour. This 
phenomenon was developed and expounded by Chevreul, who 
first described the laws by which it is regulated, and by him 
it was named contrast. 

Contrast generally shows itself simultaneously in the ob- 
servation of two or more colours side by side or close together. 
There is another form of contrast of colours, and that is, that 
when, after looking at one colour, we look at a second colour, 
in the latter case the sensation is more or less of a subjective 
character, while in the former case the sensation is of a much 
more tangible character; we may therefore distinguish, as 
Chevreul distinguished, between two kinds of contrast known 
as: — 

(1) Simultaneous contrast. 

(2) Successive contrast. 

Simultaneous contrast is that form where we see two or 
more colour effects at the same time, and as the phenomenon 
observable has a most important bearing on the practical 
Applications of colour, it will be of importance to study the 
matter in detail. We may get two forms of simultaneous 
•contrast : — 

(1) Contrast of tone. 

(2) Contrast of colours. 

(105) 



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106 THE THEOEY OF COLOUB. 

• 

By contrast of tone is meant the effect which is obtained 
when we look at or observe several tones or shades of the- 
same colour. In Fig. 9, Plate III., we have a rectangular 
space divided into six equal divisions, which are filled with six: 
different tones, from light to dark of the same grey colour- 
The experimenter may imitate this very easily by taking a 
piece of Bristol cardboard, outlining with a pencil a rectangular 
space and dividing this into six spaces ; then having mixed a 
light wash of sepia or Indian ink, brush it evenly over the- 
whole of the six divisions. This wash the experimenter allows 
to dry. He then covers up the first of the divisions on the- 
left hand and applies another wash over the remaining five ; 
this second wash is also allowed to dry. The two divisions on 
the left hand are now covered up and a wash applied to the 
remaining four divisions, and this, process is repeated until 
finally the last division has received its wash, care being taken 
that each wash shall be laid on as evenly and uniformly a» 
possible, and to facilitate this uniform washing it is recom- 
mended to cover up the left hand- divisions as each successive 
wash is applied. Now it will be observed, on looking at thi& 
tinted rectangle, that each division does not appear of a uni- 
form colour, but each has a fluted or hollow appearance^ 
although really the whole of the surface of each division is 
perfectly uniform in tint. This showc: us that, whatever may" 
be the reason, our eyes do not always see tints and shades 
exactly as they are ; and further, that the appearance of these 
tints and shades has a material influence in judging the form 
of the object observed. 

We may .get some idea of the cause of the fluted appear- 
ance represented by the six strips shown in Fig. 9, Plate III., 
by making another experiment which is shown in Fig. 1, 
Plate IV. Here are shown four strips of grey paper placed a& 
shown in the figure ; A and A^ are of a pale tint, B and B^ 
darker. Now if thiese are looked at for a short time it will be 



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CONTBAST. 



107 



noticed that a portion of A^ which is next to B^ appears to 
be paler in tint than A, while that portion of B^ which is next 
to A^ has a darker appearance than B ; it is evident, therefore, 
that if a pale object is placed next to a dark object it appears 
to be paler than it really is, and similarly a dark object next^ 



a' 

CL 


a! 


h' 


B' 
b 



Fig. 64. 
to a light object has a darker appearance than it actually is.. 
If now the middle portions of A^ and B^ are covered over as- 
shown in Fig. J54, leaving two strips of each visible, it will be- 
observed that the adjacent strips a} and 6^ have a stronger 
contrast of tone than the strips a and 6 which are removed 





Fig. 66. 

from one another. This shows us that our judgment is modi- 
fied by the degree of contiguity of the contrasting objects^ 
If we take the two strips A and B of Fig. 1, Plate IV., and 
place them at a short distance apart, as shown in Fig. 65, 4t 
will now be seen that the contrast between A and B of this- 



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108 



THE THEOBY OF COLOUB; 



last figure is by no means so great as between A^ and B^ of 
Fig. 1, Plate IV. 

This contrast of tone is observable with all colours when 
we look at different tints at the same time. The reader is 
advised to experiment on this phenomenon by using strips of 
•^coloured papers, light and dark shades of the various colours, 
and placing them in various positions, as indicated in the 
drawings. 

Contrast of Colour. — Contrasts of colour are of a much 
jnore complex character than are contrasts of tone, and are 
modified according to the relative brilliancy of the colours 
which are contrasted, they are also often open to modifications 

of a subjective character, and 
then may present contrast of tone, 
while again, in dealing with con- 
trast of tone, we have to deal 
with simultaneous, contrast. In 
regard to the contrast of colour 
we may have also to consider 
successive contrasts in addition 
to simultaneous contrasts. If, 
in carrying out the experiment which is illustrated in Fig. 1, 
Plate IV., we use two different colours as shown in Fig. 2, Plate 
IV., we make A and A^ all red and B and B^ all yellow, it will 
be seen that the appearance of A^ and B^ to the eye is not the 
same as A and B. Now it will be observed that A^ will ap- 
pear to have a more violet tone than A, and that B will have 
a greener tint than B^ It is evident, therefore, that the rela- 
tive positions of the two coloured spaces A^ and B^ have brought 
about a modifying influence upon the appearance of the coloured 
strips as represented to the eye. It inay be also shown by ar- 
ranging the strips A^ and B^ as illustrated in Fig. 66, that 
the contrast or modifying influence of one colour upon the 
other is greater if they are close together than when they 



A' 
a 


a 


h' 


h 



Fig. 66. 



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CONTRAST. 



109' 



are farther apart. By carrying out a. number of experiments 
with diflferent coloured spaces, which can be conveniently done 
by means of pieces of coloured papers or dyed cloths, neither 
of which should have any lustre, the contrasting influence of 
one colour upon another may be observed. 

The following table shows the influence which one colour^ 
exerts upon another when subjected to* this simultaneous 
contrast, taken chiefly from Rood : — 



No. 1 



L 



Colour pairs 

/Red . 

\ Orange 

fRed . 

\ Yellow 

* I Green 

fRed . 

■\Blue . 

fRed . 

*\Cyan blue 

/Red .' 

^•(Violet 

/Orange 

'•\ Yellow 

g jOrange 

*\ Green 

^ (Orange 

' (Cyan blue 

•\ Violet 

(Yellow 
*\ Green 

12 /Y«»°'' 
i^Cyan blue 

^g jYellow 

•\ Bright blue 

.. (Green 

' ^*- 1 Blue 



f Green 

^^•\ Violet 

(Greenish 
Violet 

^'•\ Violet 



•yellow 



Modification by contrast 
Inclines to violet. 

„ „ yellow. 

„ „ violet. 

,,. ,, greenish-yellow 
Becomes more brilliant. 

>> i» »» 

Inclines to orange. 

,; green. 

„ yellow. 
,, ,, blue-green. 
„ „ orange. 
„. „ blue. 
„ „ red-orange. 
„ „ greenish -yellow.. 
„ „ red-orange. 
,, „ bluish -green. 
Becomes more brilliant. 

»» »» >» 

Inclines to yellow. 

„ „ bluish. 

„ ,, bright orange. 

„ „ blue. 

„ ,, orange-yellow- 

„ „ bright blue. 
Becomes more- brilliant. 

)? n *f 

Inclines to yellow. 

„ „ violet. 

,,. „ yellow-green. 

,,. „ reddish. 
Becomes more brilliant. 

»» i» »» 

Inclines to greenish. 
,, ,, reddish. 



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110 



THE THEOEY OF COLOUE. 



If this list of pairs be examined and compared with a 
chromatic circle given in Fig. 67, particularly noticing the 
relative distances diametrically of the pairs, it will be observed 
that the effect of contrast is to throw each member of the 
pair farther apart. Thus with pairs that are already situated 
as far apart as they possibly can be, as is the case with com- 
plementary colours, the effect of contrast is to render each 
much more brilliant and distinct. 

The effect of contrast may be studied in several ways 




Fig. 67. 
other than those already mentioned : thus in Fig. 68 it may 
be shown by means of a revolving disc. This revolving disc 
is white with four coloured sectors, which may be green or 
red or yellow as desired. In the middle of the sectors are 
placed, as shown in the figure, strips of black ; on rotating the 
disc the coloured sectors will produce a coloured ground, 
while the black strips will produce a ring of grey, but it will be 
observed that this ring of grey becomes tinted with the colour 
complementary to that of the ground and contrast effects are 
thereby obtained. 



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CONTEAST. Ill 

Another form of apparatus which can be employed for 
this purpose is that devised by Ragona Scina, shown in Fig. 
69. This consists of two pieces of board placed at right 
angles to one another, and covered with white cardboard or 
white paper. From the angle where the two boards meet 
there projects at an angle of^ 45° a piece of deeply coloured 
(preferably ruby) glass. Now if the eye be placed in the 
position shown in the drawing, it will receive light from two 
sources: (1) light that is reflected from the bottom of the 




Fig. 68. 
apparatus, which passes through the coloured glass, will be 
coloured; the eye will also receive light reflected from the 
aide of the apparatus, which is reflected from the upper 
surface of the glass, and will consist mostly of white light. 
If a piece of black paper is attached to the right side of the 
apparatus, the reflection of this will be seen by the eye as if 
it formed a red patch, if the coloured glass be of a ruby tint, 
and will appear as if it were a red square at the bottom of the 
apparatus. A small square of black is placed at C ; this will 
prevent any light being reflected through the glass to the eye 



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112 



THE THEOEY OF COLOUR. 



from that particular spot, and it should make its appearance 
as a black patch ; but owing to the fact that the upper surface 
of the glass is reflecting white light, the patch shows itself as 
a grey ; but being alongside a red patch we have the effect of 
contrast, and the grey patch acquires more or less a greenish 
tint. That this is so may be shown by removing the black 
square B from the right side, when the patch C will show 
itself in its true appearance, grey on a pale red ground. If, 




Fia. 69. 

in place of employing a rqd glass, a blue glass were used,, 
then the grey patch would assume an orange-grey tint. 

A very interesting series of experiments in contrast may 
be made by producing shadows of an Object with various 
coloured lights, white, etc., and noting the tints of the shadows 
thus obtained ; for instance, if a rod of wood or metal is 
held in front of a white screen, and it is illuminated by sun- 
light from an aperture in a window, a grey shadow on a 
white ground will be produced. If now a lighted candle 
or gas flame be placed near, a second shadow of the rod, close 
to the first one, will appear ; we shall now have the appear- 
ance, not of a second grey shadow, as one would expect to be 



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(Theory of Colour). 



Colour Contrasts. 



To face p. 112. 



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CONTEAST. 113 

the case, but of a blue shadow on a yellow ground. The 
explanation of this is that the sunlight illuminates with pure 
white light the surface of the screen except that occupied by 
the shadow caused by the rod ; the candle illuminates the 
whole of the surface with a yellow light — that is, yellow in 
comparison with the sunlight— except that portion covered by 
the second shadow of the rod, and this is illuminated by white 
light, which, however, by contrast with the yellow of the 
ground, acquires a decidedly blue tint. To obtain the best 
results in carrying out this experiment it is necessary to have 
the shadows as nearly of the same intensity as possible^ which 
can be done by regulating the amount of sunlight admitted. 
If the shadows be observed through a tube the inner surface 
of which is blackened, then the shadow caused by the candle 
flame will appear to be blue, and the shadow caused by the 
white light will appear to be yellow, from the effects of con- 
trast. If now the position of the tube is changed so that only 
the blue shadow is observed, we get still the effect of blue, 
although really we are looking at white light, and have no 
means of producing contrast effects. The candle flame may 
be even screened off without affecting what is visible through 
the tube ; but if the tube, be removed from the eye, the con- 
trast effect immediately vanishes, proving that in this case the 
effect is due to error of judgment of the eye. 

Successive Contrast of Colours. — ^In- dealing with the 
phenomena of persistence of vision on page 93 we referred 
to colour phenomena in which, after looking intently at a 
coloured surface, and then transferring the gaze to a white 
surface, an after-image of the original surface was formed, but 
in a colour complementary to that originally presented to the 
eye. The phenomenon here referred to is of a subjective 
character, differing therefore from the objective sensations 
produced on the retina by the observation of tangible objects. 

The image or sensation first produced on the retina is known 

8 



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114 THE THEOBY OF COLOUR. 

as the positive image, while the after-image or sensation is 
known as the negative image. Phenomena such as those 
ah*eady alluded to have a considerable bearing on the impres- 
sion which colours produce in our eyes, especially when we 
look at a series of colours in succession ; for example, if we 
have been looking at a red object or a series of red objects 
for some time, and then turn our attention to blue objects, w^e 
find that, so far from the blue presenting its true colour to 
the eye, it acquires a greenish tint ; a white surface viewed 
in the same way tends to acquire a green tone. Such sub- 
jective phenomena are not always readily perceptible, some 
observers' eyes being more sensitive in this direction than 
othera A more elaborate illustration is the following. Close 
one eye, say the right one, and look steadily for a short time 
at a sheet of red paper — in a few minutes the brilliancy of 
the sensation will become less ; then look at a sheet of violet 
paper with the same eye — the violet paper will now appear 
to the eye to be much bluer in tone than it really is. If the 
right eye be opened and the sheet of violet paper observed, 
it will appear to be even redder in tone than it originally ap- 
peared to the left eye, the bluish-violet observed by the left 
eye contrasting with the violet tint observed by the right eye. 
Such phenomena as these are explainable as due to the fatigue 
of the special sets of colour nerves, which dull the sensitive- 
ness of the eye for those particular colours. This has been, 
explained in a previous chapter, to which the reader is referred. 
This question of successive contrast of colours, brought 
about by first looking at one colour and then kt another, has 
a very important bearing on the judgment of the actual colour 
of coloured objects. It is a fact well known to persons who 
have to examine dyed or printed goods of the same colour, 
that the eye loses its sensibility, so that after a time it does not 
perceive the objects in their true colours ; not only so, but if 
the observer passes through a range of goods of one colour, 



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CONTENT. 



115 



say red, quickly to a range of goods of another colour, say 
blue, then the latter is much influenced by the colour effect 
left by the former. The following table will give some idea of 
the modification of colour which is brought about by the suc- 
cessive observation of different colours : — 



If the eye I 


las first seen and then looks at 


the latter colour will appear. 


Bed Orange . 


. Yellow. 


Bed. 






. Yellow . 


. Greenish-yellow. 


Bed. 






. Green . 


. Bluish-green. 


Bed, , 






. Blue 


. Greenish-blue. 


Bed. 






. Violet . 


. Bluish-green. 


Orange 






. Bed 


. Beddish-violet. 


Orange 






. Yellow . 


. Greenish-yellow. 


Orange 






. Green 


. Bluish-green. • 


Orange 






. Blue 


. Tinted with violet. 


Orange 






. Violet . 


. Bluish- violet. 


YeHow 






. Bed 


. Beddish-violet. 


YeUow 






. Orange . 


. Ueddish-orange. 


Yellow . 




' 


. Green 


. Bluish-green. 


Yellow 






. Blue 


. Violet-blue. 


Yellow • 






. ■ . Violet . 


. Bluish-violet. 


Green 






. Red 


. Tinged with violet. 


Green 






. Orange . 


. Beddish-orange. 


Green 






. Yellow . 


. Orange-yellow. 


Green 






. Blue 


. Violet-blue. 


Green 






. Violet . 


. Beddish-violet^ 


Blue 






.Bed . . 


, Orange-red, 


Blue 






. Orange . 


. Yellower, 


Blue 






. Yellow . 


. Orange-yellow. 


Blue 






. Green . 


. Yellowish-green. 


Blue . 






. Violet . 


. Beddish-violet. 


Violet 






.Bed . . 


. Orange-red. 


Violet . 






. Yellow . 


. Slightly greenish. 


Violet 






. Orange . 


. Yellowish-orange. 


Violet . 






. Green 


. Yellowish-green. 


Violet . 






. Blue 


. Greenish-blue^ 



Some colours produced by successive contrast are much 
more distinct and persistent in their appearance than others ; 
for instance, when the eye has looked at red and then at green, 
the change to bluish-green is brought about immediately. 
Again, if after having looked at violet we fix the eyes on 



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116 THE THEORY OF COLOUR. 

yellow, the contrast effect is clear and remains ; while the con- 
trast effect of blue and orange is intermediate between these 
two pairs. It should also be p6inted out that the depth or 
tone of the contrasting colours has a very material influence 
upon the effect produced. If the eye has first looked at a 
reddish-orange and then proceeds to view dark blue, the latter 
may exhibit, a greenish effect ; while, on the other hand, 
normal blue following on normal orange would become more 
violet. 

There is another effect of contrast to which attention may 
be usefully directed at this point. When we have uniform 
masses of two colours placed side by side as shown in Fig. 3, 
Plate IV., we get the effect of contrast on both these colours 
comprised within the rules laid down. When, however, the 
mass of colour is in the form of fine lines or dots, placed side 
by side, such as shown in Fig. 4, Plate iV., then viewed from a 
little distance, the eye fails to distinguish between the separate 
lines or points, the effect of contrast being greatly heightened ; 
and in place of seeing the lines or points, one has the effect of 
a mass of colour, a combination of the colours employed. Thus 
when the colours are red and blue the effect produced is violet ; 
when they are blue and yellow, green is the result. This pro-' 
perty which colom^s have of mingling is taken advantage of 
in decorative work by printing or producing, side by side, fine 
lines or dots of colour, or by overprinting the lines of one 
colour with those of another, to produce colour effects which 
could not conveniently be obtained by the direct admixture of 
the pigments themselves. 

This property of contrast is made use of very largely by 
^designers of figured textile fabrics, who, by a judicious arrange- 
ment of the warp and weft threads, can, by using only three 
different coloured threads, produce a design in six tints. For 
example, by using red, white and blue threads in both warp 
3nd weft a figured design in dark red, pink, dark blue, light 



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CONTRAST. 117 

blue, violet and white, may be produced, the dark red being 
formed by the crossing of red warp and weft threads, the pink 
by the crossing of red and white threads, the dark blue by the 
crossing of blue warp and weft threads, the light blue by the 
crossing of blue and white threads, the white by the crossing 
of white threads, and the violet by the crossing of red warp 
and blue weft threads. Other combinations of colour and 
effect are produced, by using other coloured yarns. 

Colour Contrast in Decorative Design. — Colour contrasts 
have a most important bearing upon decorative design in 
whatever way the contrast effects may be brought about — 
in the production of wall papers and wall hangings, in calico 
printing, in weaving coloured figure cloths, the designing of 
carpets and floor cloths, in painting, and wherever Inhere are 
brought into juxtaposition several colours which are viewed 
at the same time. We must therefore devote a considerable 
amount of attention to the influence or contrast efleet pro- 
duced by one colour upon another from a practical point of 
view. Chevreul, who was one of the first to observe the 
effects of the simultaneous contrast of colour, was induced to 
do so by being consulted in a case in which the merchants 
refused some printed calicoes on the ground that the colours 
were not equal to pattern, besides being deficient in depth, 
pointing out that the blacks were of various tints in the dif- 
ferent fabrics. The printers said this could not be the case, 
inasmuch as all the patterns were printed with fdie same black 
and therefore should have been identical ; that while some of 
the designs were approved of others were rejected, but they 
averred the colours in these were identical with those which 
were accepted* By cutting out pieces and comparing them 
independently of the designs of the goods, Chevreul showed 
that they were identical and of the required degree of strength, 
that therefore the effect of the difference in colouring was due 
to the influence of one colour upon the other when placed 



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118 THE THEOEY OF COLOUB. 

together in the design : the black when placed against the red 
showed a greenish hue, while placed against a green it acquired 
a reddish tint ; moreover, a black placed against a bright colour 
appeared somewhat impoverished. 

Plate V, illustrates the effect of various grounds upon 
diflferent colours. There are four ^grounds — white, black» 
yellowish-grey and bluish-grey ; taking the various colours 
we see that the red on white ground appears brilliant and 
deep, while the ground itself has a tendency to acquire a 
greenish tint ; orange looks bright and brilliant in tone, yellow 
becomes darker, is less luminous, and is not prominent, and, if 
anything, shows a tendency to acquire a greenish tint ; deep 
yellow on white is much more satisfactory than pale yellow on 
white. The contrast between orange and white is greater than 
that between yellow and white^ and is much more effective. 
Green on a white ground appears to become more intense and 
of a deeper tone, white evidently improving its appearance. 
Blue on a white ground shows a better and deeper appearance, 
the effect being more striking with deep blues than with pale 
blues. Violet on white shows a decided contrast, and is en- 
riched considerably. It will be observed that the general 
effect of a white ground is to deepen and enrich the coloura 

A black ground being very much deeper in tone than any 
colour, when employed as a groundwork its presence tends to 
lower the tone of the contiguous colour, while at the same time 
its own tone becomes modified. Now, as all black surfaces 
reflect a little white light, the black becomes tinted with the 
complementary of any colour with which it may be contiguous. 
There is one important fact to note, and that is, if the con- 
tiguous colour be deep in tone, blue or violet and some shades 
of deep red, the black tends to appear slightly weaker. Red 
on black has a tendency to become more luminous, and to ac- 
quire an orange tone, the black having a greenish tint. 
Orange and black become much more luminous, and of a 



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CONTEAST. 119 

yellower tone, the black appearing to be of a bluer shade. 
Yellow on black is one of the greatest contrasting changes 
that can be produced ; .the yellow becomes lighter and much 
more luminous, while the black has an enriched appearance, 
due to its acquiring a bluish-violet hue. Green on black 
becomes more brilliant, but rather lighter in tone; on the 
other hand, the black acquires a rusty hue and appears im- 
poverished, owing to its becoming tinged with the complemen- 
tary colour red. Blue on black is a rather poor combination, 
especially when the blue is of a deep tone, the black becoming 
slightly rusty in tone ; a light shade of blue becomes a little 
more luminous on a black ground. Violet on black becomes 
slightly (?eeper and richer in tone, but, on the other hand, the 
black loseis some of its intensity and acquires a rusty hue. 

Colours on grey will vary considerably according to the 
tone of the ground, for the name grey is a vague one, and is 
applied to various tints and shades markedly different in 
character ; thus, in Plate V., there are also given two shades 
of grey ground — a yellowish-grey and a bluish-grey — and it 
will be observed that the effect of these two kinds of grey 
grounds on the various colours is different. Taking the 
yellowish-grey we note the following, that red becomes some- 
what more intense and deeper, and acquires a bluish hue ; 
orange becomes redder in tone ; yellow becomes darker and 
rather less luminous, much depending upon the relative in- 
tensities of the yellow and the grey, pale grey having a ten- 
dency to reduce the luminosity of the yellow, while the deep 
grey increases it ; green becomes* somewhat deeper and bluer 
in tone ; blue becomes much brighter in tone and is enhanced 
in quality, while violet becomes somewhat bluer in tone and 
brighter in appearance. With the bluish-grey somewhat dif- 
ferent results will be obtained. The red becomes brighter 
and somewhat yellower in tone ; orange is made a little more 
luminous and forms a very good combination ; yellow is 



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120 THE THEOKY OF COLOUR. 

• 

rendered more luminous and deeper ; green is rendered lighter 
and somewhat yellower in tone ; violet is somewhat deadened 
in appearance; while there is little effect on the blue, which, 
if anything, is rendered slightly less luminous. These experi- 
ments will suJQ&ce to show th^t contrast has a very material 
influence on colours when they are employed in a decorative 
design. In another chapter some further consideration will be 
given to the subject of colour from a decorative point of view. 

Theories of Contrast. — At the present time there are two 
theories which have been put forward to ^explain the pheno- 
mena of colour contrast — the psychological theory of Helmholtz 
and the physiological theory of Hering. 

The psychological theory of Helmholtz supposes the exist- 
ence in the eye of three sets of colour-nerves corresponding to 
the three primary colours ; these have been alluded to in the 
last chapter. Now a colour not only excites that set of nerves 
which are peculiar to it, if it be a primary colour, or if it be a 
secondary colour the nerves corresponding to the primaries of 
which it is composed, but also, although to a lesser degree, 
the nerves of the colour complementary to it ; a red colour 
will thus not only excite the nerves sensitive to red but also 
affects the nerves sensitive to the complementary colour green, 
although in a minor degree. Both sets of nerves transmit the 
sensations which have been excited in them to the brain. The 
latter, however, does not distinguish between the red sensation, 
which is the real objective colour sensation, and the green, 
which is a subjective sensation, but only sees, as it were, one 
colour, which must naturally be composed of two colour sensa- 
tions, and will therefore be modified accordingly ; thus a red 
will look somewhat yellower than it really is, for red and 
green colours give rise to yellow. In the same way green 
will appear rather more bluish and a blue more greenish than 
it really is. Yellow will appear brighter, because it brings 
into play all the colour nerves, and therefore excites a sensa- 



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CONTEAST. 121 

tion of white light in the brain, which makes the colour ap- 
parently brighter than it otherwise would have been. When 
we see two colours side by side, as in Fig. 2, Plate IV., the 
three sets of colour nerves are excited at the same time, we 
therefore do not see either colour as it really appears, but in a 
modified manner; hence we get what are called contrast 
effects, which have already been described. 

The physiological theory, to which Hering has given his 
support, supposes the existence in the retina of the eye or in 
the retina-cerebral substance, of a material which is called 
"vision stuff" (" Seh-Stoff "), and that by the aid of this 
material the various colour effects are brought about by 
chemical changes; for instance, the red changes the vision 
stuff in one direction, green in another, and so on. These 
changes are considered to be of two classes, one the 
assimilative or anabolic, which is induced by black, blue 
and green colours; while in the second the changes are 
dissimilative or catabolic, and are produced by white, yellow 
and red colours, and further, these changes may extend out- 
side the area directly influenced by the colour cause. One 
experiment, on Which Hering relies as support for this theory 
can be made as follows : On a large sheet of paper place 
side by side a large piece of black and a large piece of 
white paper, the division between the two patches being 
vertical. Fixed in the centre and touching the vertical 
division attach two V-shaped pieces of grey paper with 
apices touching one another, one of the V*s being on the 
black, the other on the white. Look intently at the two 
V s for a short time, and then turn the eye to a uniform white 
surface, upon which will be seen after-images of the black 
and white papers, and of the two grey V's ; the after-image 
of the black and white papers will soon disappear, while 
that of the V on the black ground appears to be darker than 
that of the V on the white ground. In explanation of this 



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122 THE THEORY OF COLOUR. 

phenomenon, Hering considers that it must be due to a 
material change brought about by the Vs in a portion of 
the retina-cerebral portion of the eye. This chemical theory 
seems, however, to postulate the presence of a substance not 
hitherto found in the eye, which must be exceedingly sensi- 
tive to light reactions. On the other hand, the psychological 
theory of Helmholtz does not presume the presence of any- ^ 
thing other than what is known to be present in the retina, 
or assume any changes in the nervous system of the eye 
which are at all problematical. 



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^, CHAPTER VL 
COLOUR IN DECORATION AND DESIGN. 

Colour plays a very important part in the decoration and 
•design of houses and public buildings, in the ornaments with 
i«rhich we surround ourselves, and the materials employed in 
•our clothing. 

The simplest colour effect is produced when a single 
•colour is alone employed, but such colour effect varies in 
the impression it makes upon our eyes, or, perhaps, more 
•strictly speaking, upon our sense of coloun The sense of 
•colour varies in different individuals — in some it is more 
(highly developed than in others ; we find therefore that a 
-colour or combination of colours makes a different impres- 
sion upon one individual than it does Jon another, so that it 
may be pleasing to one although far from harmonious to 
another. In this respect the sense of colour resembles the 
■sense of sound : a combination of musical notes which grates 
fupon the ears of one person, whose sense of musical harmony 
is strongly developed, would pass unnoticed by one whose 
sense of music is in a rudimental condition. 

The impression which a colour makes upon the eye de- 
pends upon several factors — first its character, whether it 
be red, orange, yellow, green, blue or violet; whether it 
18 brilliant or luminous, dull or sombre. Different colours 
4J80 convey particular impressions to the mind, yellow, for in- 
stance, conveys i?he impression of luminosity or brightness. 
£lue, on the other hand, conveys the impression of coldness ; 

(123) 



^ 
\ 



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124 THE THEORY OF COLOUR. 

again, red conveys the impression of warmth. Hence it is 
that artists, when they wish to give a bright tone to their 
pictures, or desire to impart a brightness or warmness to- 
the decoration of a room, employ reds or yellows; while, 
on the other hand, blues and violets, conveying as they do- 
the feeling of coldness, are always used when such an 
impression is desired. Then, again, colours convey an im-^ 
pression of distance; thus red and yellow always convey 
an impression of nearness, while blues and greens convey 
an impression of distance. This is observable on Plates VI. 
and Vin. in which a number of combinations of colours are- 
given, it will be noticed that the yellow and red parts appear 
to stand out much more prominently than the greens, blues 
or violets. Artists are well acquainted with this fact, and 
always, in painting landscapes, give a blue tone to the distant 
objects of the picture, while this is brought into tsontrast 
by a reddish tint which the nearer objects are naade to- 
assume. 

In any scheme of decoration, when two or more colours 
are employed in producing the effect, we have the question 
of contrast entering into the case, the combinations of colours- 
having a harmonious or inharmonious effect upon our sense^ 
of colour. When we have two colours the simplest possible case^ 
of colour contrast is presented ; when, however, there are more 
than two colours, the colour effect becomes more complicated^ 
and the diflBculties of producing a harmonious colour scheme 
are increased. On Plate VI. is given a design repeated several 
times in different combinations of colours, which will illustrate 
the remarks on the harmony of contrast which are given 
below. The reader examining this plate is advised to cover 
up those portions of the plate which is not under examination,, 
so that there is simply in view a particular colour combina 
tion that he wishes to observe, in order to* avoid any effect 
of contra u with the other portions of the plate. The fol 



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♦ 

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COLOUE IN DECOKATION AND DESIGN. 



125 



lowing tables contain a number of pairs of colour combina- 
"tions, together with the effect produced on our sense of colour 
liarmony. Before studying these tables it may be pointed out 
that much depends upon the tone and brilliancy of the respec- 
-tive colours ; thus, for instance, the juxtaposition of a crimson 
-with a yellow is a very inferior combination, but if the red 
inclines to a purplish tint and the yellow to a greenish, the 
•combination becomes a fairly good one. 



HABMONY OF TWO COLOUR CCMBINATIGNS. 



Crimson and orange 
„ yellow 
„ green 
„ blue . 
„ violet 
» t> gold-yeUow 
-Scarlet and yellow . 
„ green . 
„ - „ greenish-blue 
„ „ blue . 
„ „ violet . 
•Orange and yeHow 

„ „ yellow green 

„ „ green . 

„ ,., green-blue . 

„ blue . 
,, „ violet . 
Orange-yellow and crimson 
„ scarlet 
„ green 
„ blue-green 
„ green-blue 
„ blue 
,, violet 
Yellow and crimson 
„ green . 
., „ blue-green 
„ „ blue 
„ „ violet . 
<Green and blue 
„ „ violet 
,, red 



Bad. 

Inferior. 

Strong but harsh. 

Good. 

Bad. 

Good. 

Bad. 

Inferior. 

Good. 

Good. 

Bad. 

Poor. 

Fair. 

Strong poor. 

Fair. 

Good. 

Strong-good. 

Poor. 

Poor. 

Bad. 

Bad. 

Fairly good. 

Excellent. 

Good". 

Poor. 

Bad. 

Very bad. 

Only fair. 

Very good. 

Very poor. 

Moderate. 

Good. 



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126 



THE THEORY OF COLOUR. 



From a coDsideration of the above tables the following- 
rules may be laid down : First, that two colours which are 
closely related to one another do not form a harmonious pair- 
— as, for instance, red and orange, and blue and green 
This may be observed by comparing the two star designs^ 
Nos. 4 and 7 on Plate VI. ; on the other hand, blue and red, 
green and violet, and also yellow and violet go well together, 
as may be seen on comparing the numbers 2, 3 and 5 on the^ 
same plate. Much, of course, depends upon the tone and 
brilliancy of the colour, as previously pointed out. 

The following table gives some combinations of pigments, 
and colours and their eflfect, which may be of service to artists- 
and designers : — 



Orange and ultramarine 
Lemon-yellow and ultramari 
„ ,, vermilion 
Emerald green and violet 
„ purple 
„ red . 


ne 








Good and strong 
. Moderate. 

Strong and hard. 

• »» >» »♦ 

• »♦ »» »» 
»♦ »» »» 


„ „ orange 
„ yellow 
Ultramarine and carmine 










»» »» »> 
. Bad. 
Poor. 


„ purple 
„ violet. 
Violet and carmine 










(f 



On looking at designs Nos. 4 and 7, in which colours are 
used that are related to one another, it will be noticed that 
they are indistinct, this indistinctness arising from the effect 
of simultaneous contrast on the two colours tending to blend 
them one into the other. By interposing between them 
either black or white, however, the distinctness of the colours- 
is materially increased, as may be observed on comparing 
Figs. 5 and 8, in which the following colours, blue and green, 
and emerald-green and dark green, have been used, but are^ 
separated by black in one case and white in the other. 

There is another feature of colour which enters into the 



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COLOUR IN DECORATION AND DESIGN. 127 

production of a harmonious colour combination, and that is 
what may be termed the f ulhiess and relative proportion of 
the two colours which are used ; thus, for instance, while a 
colour combination of blue and yellow, in which the blue 
largely predominates so far as the amount of space occupied 
is concerned, may be harmonious, on the other hand a 
combination of the same two colours, in which the yellow 
predominates, may have a displeasing effect — the yellow, on 
accoimt of its greater luminosity, overpowering the effect of 
the blue. No very definite rules can be given bearing on 
this point, so much really depending upon the tone of the 
particular colours entering into the combinsition. 

Field has endeavoured to lay down proportions between 
the various colours — as, for instance, he says that 3 parts of 
yellow are equal to 5 parts of red, or to 8 parts of blue, or 
that 11 parts of green formed by the combination of 8 parts 
of blue and 3 of yellow will equal 6 of red, or again that 13 
parts of purple formed by the combination of 8 of blue and 5 
of red, will balance 3 of yellow. But all such attempts at 
colour relations are purely arbitrary, and only true of certain 
particular shades or tints. No definite rules can be given by 
means of which the designer can with geometrical accuracy 
proportion the several areas of the different colours that he 
uses, and he must, in developing his designs, find the proper 
balance of colour by trial with the pigments he may be using. 

When more than two colours are used in a design, the 
production of a harmonious contrast becomes much more 
diflBcult. The combination of crimson, yellow and blue is 
good ; as also is one of purple, yellow and greenish-blue ; or 
orange, green and violet. A combination of green, yellow and 
crimson is rather harsh ; one of red, yellowish-green and violet- 
blue is good ; while one of red, green and blue is rather poor. 
In colour combinations of this character, by separating them 
with white or black, the effect becomes much more pleasing. 



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128 THE THEORY OF COLOUR. 

Chevreul lays down the following propositions as explain- 
ing the harmonious contrast of colours. 

Ist Proposition. — In the harmony of contrast the comple- 
mentary arrangement is superior to every other. 

2nd Proposition. — The primaries red, yellow and blue, 
associated in pairs, will assort better together as a harmony 
of contrast than an arrangement formed of one of these 
primaries and of a binary colour, of which the primary may 
be regarded as one of the elements of the binary colour in 
juxtaposition to it. 

3rd Proposition. — The assortment of red, yellow or blue 
with a binary coMur which we may regard as containing the 
former, contrast the better, as the simple colour is essentially 
more luminous than the binary. 

4th Proposition. — When two colours go badly together it 
is always advantageous to separate them by white. 

5th Proposition. — Black never produces a bad effect when 
it is associated with two luminous colours. It is therefore 
preferable often to white, especially in an assortment where 
it separated the colours from each other. 

6th Proposition. — Black, in association with sombre 
colours, such as blue and violet, and with broken tones of 
luminous colours, produces harmony of analogy, which in 
many instances may have a good effect. 

7th Proposition. — Black does not associate so well with 
two colours, one of which is luminous, the other sombre, as 
when it is associated with two luminous colours. 

In the first instance the association is much less agreeable 
in proportion as the luminous colour is more brilliant. 

8th Proposition.-;-If grey never produces exactly a bad 
effect in its association with two luminous colours, in most 
cases its assortments are nevertheless dull, and it is inferior 
to black and white. 

9th Proposition. — Grey, in association with sombre 



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Plate X. 




(Theory of Colour). 



Colour Contrasts. 



To face p, 128. 



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COLOUR IN DECORATION AND DESIGN. 129 

colours, such as blue and violet, and with broken tones of 
luminous colours, produces harmonies of analogy which have 
not the vigour of those with black; if the colours do not 
combine well together, it has the advantage of separating 
them from each other. 

10th Proposition. — When grey is associated with two 
colours, one of which is luminous, the other sombre, it will 
perhaps be more advantageous than white, if this produces 
too strong a contrast of tone ; on the other hand, it will be 
more advantageous than black, if that has the inconvenience 
of increasing too much the proportion of sombre colonics. 

11th Proposition.— If, when two colours combine together 
badly, there is in principle an advantage in separating them 
by white, black, or grey, it is important to the effect to take 
into consideration : — 

(1) The height of tone of the colours, and 

(2) The proportion of sombre to luminous colours, includ- 
ing in the first the broken brown tones of the brilliant scales, 
and in the luminous colours, the light tone^ of the blue and 
violet scales. 

It has already been pointed* out that the harmony of a 
combination is much increased by the luminosity and tone 
of the colours forming the combination. The material on 
which the colours are placed has also a considerable influence 
on the result. A combination which is fairly good on materials 
such as stained glass and silk, which have a lustre of their 
own, may be very poor on such materials as cotton or wool, 
or in tempera painting. But on the question of the influence 
of material in the harmony of colour more will be said in a 
subsequent section. 

In regard to the use of black and white for the purpose 

of separating colours the following hints may be found useful : 

With red and yellow, black is preferable to white ; with red 

and blue, white is to be preferred ; with blue and yellow a 

9 



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130 THE THEORY OF COLOUR. 

grey is preferable to either black or white; with yellow or 
orange, black agrees very well. Grey separates blue and 
violet better than either black or white ; black should be 
used with orange and green, grey in connection with violet, 
while white can be used to separate violet and green. As 
to whether black, white or grey will give the best results in 
outlining or separating the various colours of a design, much 
depends upon the balance of tone of the colours used. The 
following rules will be found to generally cover all cases of 
colour combination with which the designer has to deal : 
(1) if the ground of an ornamental design be of a light tint 
or tone of colour, and the design itself be deep or intense in 
colour, then it will be found best to outline the design in 
black or in grey, or in a colour which is deeper than either 
the ground colour or the design colour; (2) in the case 
of an ornamental design, where the figure is of a lighter 
colour, or a less intense colour than the ground, then it will 
be found best to outline the figures with white or with a light 
shade of grey; (3) in monochrome work, where the ground 
and the design are in varying shades of the same colour, 
similar rules must be observed. If the ground be dark then 
the outlines should be white or grey; if the ground be light 
then the outlines should be of a darker shade than the general 
colour. 

The effect of separating colours by outlines is shown in 
a number of the figures given on Plate VI. and in the design 
shown on Plate VIII., and the effect of using both black and 
white for the separation of the same colours is shown on 
both plates. 

The harmony of a design or combination formed of such 
simple colours as red, yellow, blue, green, orange and violet 
is readily perceptible, but such is not the case with the 
more complex hues or shades of browns, olives, bronzes, etc. 
The differences which exist between these shades need a 



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COLOUR IN DECORATION AND DESIGN. 131 

well-trained eye to distinguish them, and to appreciate the 
harmony of any colour combinations in which they may 
enter. In nature often one meets with such combinations 
among the trunks and foliage of trees — as, for instance, the 
greyish-greens of lichens which grow on the trunks of the 
trees and contrast with the brownish tints of those members. 
Or we have the dark tints of the trunks and stems in contrast 
with the green of the leaves. Then, again, in autumn we 
get the russet tints which prevail among the foliage of the , 
trees, helping to form combinations of hues which have a 
most harmonious appearance. Language almost fails to de- 
scribe such effects, while it needs a master artist to depict 
them with the brush. 

Following on the lines first developed by Chevreul, it is 
usual to divide harmonies of colour into two classes : — 

(1) Harmonies of analogy, and 

(2) Harmonies of contrast, 

each of which can be further divided into sub-groups, as will 
presently be seen. It is, however, a more or less arbitrary 
classification, for by the term harmonies of analogy is gener- 
ally meant the effect produced by the employment of various 
tones or shades of the same colour, or what might be termed 
analogous colours; while by the term harmonies of contrast 
is meant the effect produced by the combination of different 
colours, but the two kinds of harmony often pass insensibly 
into each other. If various shades of yellow and green 
are employed, they may pass so insensibly from one to the 
other, that we get the harmony of analogy rather than the 
harmony of contrast. 

Chevreul gives the following classification : — 

HARMONIES OP ANALOGY. 

(1) Harmony of scale, which is produced when several 
tones of the same colour are present. These tones may be 



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132 THE THEOBY OF COLOUR. 

either so graded as to run insensij^ly into one another, when 
we have the effect generally known as shading, or the differ- 
ence may be rather more marked ; when the interval between 
two contiguous tones is greater, the effects of harmony of con- 
trast may also be observable. 

(2) The harmony of tones or hues. This results when two 
tones or hues of about the same degree of intensity and power, 
but belonging to different scales or different colours, are com- 
bined together. In some such cases the effect may be displeas- 
ing rather than harmonious. 

(3) The harmony of dominant colour. This effect is 
obtained when a landscape or picture is viewed through a 
lightly tinted glass, so that the colours of the objects 
are readily perceptible, although they are dominated by the 
tint of the glass, or the material through which they are 
observed. 

HARMONIES OP CONTRAST. 

(1) Harmony of contrast of scale is obtained when two 
tones of the same colour some distance from one another 
are simultaneously observed. 

(2) The harmony of contrast of hues or tones is produced 
by the simultaneous view of tones of different heights or 
depths belonging to relative colours' or scales. 

(3) The harmony of contrast of colours of different kinds, 
arranged according to the law of contrast which has already 
been discussed. 

This classification, due to Chevreul, being rather an arti- 
ficial one, is somewhat forced in character ; a much simpler 
classification, one in two kinds of colour harmony only, may 
be substituted. If particular notice is taken of the harmonies 
which prevail in nature, in paintings, and in high-class orna- 
mental designs, it will be found that harmony can be produced 
in two ways : first, by employing tones or hues of the same 



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COLOTJE IN DECORATION AND DESIGN. 133 

colour or of Colours which are related to one another; and 
second, by the use of different colours which harmonise with 
one another. For shortness we may speak of this as — 

(1) Harmony of succession, or seriation of tones or hues. 

(2) Harmony of change of colour. 

The harmonies of the first kind are often met with in 
nature in the petals of flowers, a-lso more particularly in the 
colours of the leaves in the autumn. We may have a succes- 
sion of hues passing imperceptibly one into tjie other, as 
shown in Plate IX. One sees these effects more particularly 
in large leaves like, those of the oak, horse-chestnut, and the 
•elm. Another example of such harmony would be when we 
have a succession of tones in red, orange and yellow, or of 
blue and green, passing insensibly from one to the other. Not 
only do we find such harmonies of succession or seriation 
in nature, but the artist finds them extremely serviceable for 
the production of decorative and ornamental designs for a 
variety of objects. 

That this is so one may readily see by visiting museums 
such as those at South Kensington, Liverpool or Salford, and 
inspecting the great collections of pottery ware, textile fabrics, 
and ornamental work of all kinds which are exhibited there, 
when it will be seen that the designers of them have made 
full use of the kind of harmony which we have here called 
seriation. 

The infinite gradation of shades which are met with in 
nature, producing many exceedingly charming effects, are due 
not only to changes in the general colour of the objects such as 
we have been already describing, but also to the play of light 
upon them. Artists have to take into account the peculiar 
action of light when portraying a large surface. Supposing, 
for instance, an artist wishes to depict a large sheet of white 
paper, or a screen of coloured drapery: if he were to paint 
them of a uniform white, or of a uniform colour, although he 



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134 THE THEOKY OF COLOUR. 

would be representing them as they apparently are, yet we 
should feel that something was wrong. This is due to the 
fact that the white paper or the coloured drapery is not re- 
flected to our eyes, or does not appear to us to be of a perfectly 
uniform tone ; the play of light upon it leads to the production 
of minute gradations of light and shade, which influence our 
sense of observation. The artist taking this into consideration ,. 
accordingly portrays the white paper or the coloured drapery 
with some gradations of light and shade. 

All the best artists are well aware of this important fact,, 
and pay very particular attention to it. John Ruskin, in 
his Elements of Drawing, draws attention to the importance 
of gradation of tone, apd gives this advice : " And it does not 
matter how small the touch of colour may be, though not 
larger than the smallest pin's head, if one part of it is not 
darker than the rest, it is a bad touch ; for it is not merely 
because the natural fact is so that your colour should be 
graduated ; the preciousness and pleasantness of colour depends 
more on this than on any other of its qualities, for graduation 
is to colours what curvature is to lines, both being felt to be 
beautiful by the pure instinct of every human mind, and both, 
considered as types, expressing the law of gradual change and 
progress in the human soul itself. What the difference is in 
mere beauty between a graduated colour and an ungraduated 
colour may be seen easily by laying an even tint of rose colour 
on paper and putting a rose leaf beside it. The victorious 
beauty of the* rose as compared with other flowers depends, 
wholly upon the delicacy and quantity of its colour-gradations,, 
all other flowers being less rich in graduation, not having so- 
many folds of leaf, or leSs tender, being patched and veined 
instead of flushed." 

In monochrome work the succession of tones is of import- 
ance in the production of a pleasing and effective picture; 
when a picture in monochrome work is composed simply of 



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COLOUR IN DECORATION AND DESIGN. 135 

light and dark shades, the effect is extremely harsh and dis- 
pleasing, the art and skill of the painter in monochrome work 
depends upon the careful gradation of one shade or tone into 
another. 

Another phase of the harmony of succession or seriation 
may be mentioned in the spectrum, we have a series blended 
one into the other — we may therefore have a perfect design in 
which the colours are in the following order: green, blue, 
violet, red, orange. 

A design in which the following colours are used — green, 
violet and orange — will be somewhat ineffective ; but by intro- 
ducing the intermediate colours, blue, red and yellow, the 
design will be made much more complete in character. If 
these series of colours are not sharply defined by means of 
outlines, they must shade one into the other, as in the case of 
the spectrum colours. Much of the harmony here depends 
upon the relation of form, and the definition of that form by 
means of outlines, as for instance in foliage of various tints, 
combined with flowers of different colours. This kind of 
harmony of succession of colours is very much used in artistic 
work, but in designing considerable care and skill must be 
exercised, in order to produce a perfectly harmonious result. 

The subject of harmonies of change of colour has already 
been dealt with fully in treating upon the contrasts of colour, 
therefore little need be said about it here. 

Harmonies of change of colour are greatly influenced by 
the character of the colours themselves, their relative propor- 
tions, and the employment and method of using separating 
lines of black, white or grey, to define the form and extent of 
the colours. These questions have already been referred to, 
and the influence of separating them discussed. 

In Plates VI., IX., X., and XI. are shown designs similar 
to those employed in textile fabrics, wall papers, eta They 
have been arranged to illustrate the principles of colour 'as 



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130 THE THEOBY OF COLOUR. 

applied to decorative design laid down in the preceding sec- 
tions. In Plate VI. we have the same design in a number of 
harmonies and otherwise, showing the effect of one colour on 
another. In Plate IX. we have a design comprising the 
colours orange, yellow, and yellowish-green, showing the har- 
mony introduced by using a series of colours in succession. 

In Plate X. we have a design in various tints of red, show- 
ing a harmony in tones which is rather pleasing. In Plate X. 
we have a design combining blue, green and violet, the result 
of which cannot be considered very harmonious. 

ILLUMINATION AND COLOUR. 

We have seen in a preceding section, page 65, that the 
appearance of a colour, or colours, varies according to the cir- 
cumstances or conditions under which it is observed. It will 
be useful here if we devote a little. more attention to this as- 
pect of light and colour, and consider the modifying influence 
which different kinds of illumination have upon colours of 
objects under observation. 

It must be obvious to any one that the kind and degree of 
luminosity — or, in other words, the quality and intensity of 
the light which falls upon objects — varies from time to time, 
and it is a matter of common observation that the appearance 
and tint of the colours of such objects vary in a correspond- 
ing degree. We shall subsequently see that the character of 
the surface of the object also has some influence on its appear- 
ance. 

Objects may be observed under at least four kinds of illu- 
minants : — 

(1) Direct sunlight or diffused daylight. 

(2) Artificial light. 

(3) Dominant coloured light. 

(4) Two lights of varying quality and intensity. 

(1) It is a matter of common observation that daylight 



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COLOUR IN DECORATION AND DESIGN, 137 

varies much in colour, not only during each day, but at differ- 
ent seasons of the year. The cause of this variation in colour 
in the light is due to the fact that the atmosphere through which 
the light travels to the earth in its passage from the sun is 
never perfectly transparent, but is always more or less 
clouded in character, the degrees of cloudiness varying from 
that of a clear bright summer's day to that of a foggy winter. 
Now, when light passes through a cloudy medium, it under- 
goes a change which varies in degree according to the character 
^nd extent of the cloudiness. If a mass of water be observed 
against a black background it will appear perfectly transparent 
. 4ind colourless, but introduce into it a small quantity of milk or 
finely powdered chalk, then the water will appear of a bluish 
colour ; the milk or. the chalk forms a cloudiness in the 
water, which has the property of reflecting the blue rays of 
the spectrum to a greater extent than the rays at the red end of 
the spectrum, and hence the water appears of a bluish hue. It 
is for the same reason that the sky appears of a blue colour 
when observed under ordinary conditions; the atmosphere is 
filled with minute particles, which reflect chiefly the blue rays 
•of the sunlight, and these blue rays make the sky appear blue. 
The same phenomenon may be observed in all cases where light 
is reflected from a medium more or less cloudy, placed against 
a black background. The question of the colour of a cloudy 
medium is dependent upon the degree of the cloudiness ; should 
the cloudiness increase considerably and the light be ob- 
served more directly, then the reflected rays which are bluish, 
being reflected in all directions, while the other rays of the 
spectrum are transmitted in greater proportion, the blue rays 
tend to lose their ascendancy, therefore the light which is 
transmitted through a cloudy medium assumes an orange tone. 
It is for this reason that sunlight, when observed through a 
foggy atmosphere, appears of a red colour ; and also the sunset 
hues appear of a red character, because they are transmitted 



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138 THE THEORY OF COLOUR. 

through a greater thickness of atmosphere than is the ease when 
the sun is more directly overhead, as it is at noonday. Street- 
lamps, for the same reason, have an orange colour on a foggy day ^ 
the particles of aqueous vapour, etc., which constitute the fog, 
having a sifting action upon the light from the lamps — the 
blue rays are reflected and scattered in all directions, while 
the orange and yellow rays are transmitted. 

There is another feature of a cloudy medium which must 
also be noticed; if a ray of light be transmitted through clear 
water, it will pass through practically unchanged, the water not 
being greatly illuminated as a whole ; but on placing a small 
quantity of milk in the water, immediately the whole tankfuL. 
becomes more or less illuminated with a diffused light which is 
of a bluish character if viewed by reflect€tfi light, or of a yellow- 
ish or orange tone if observed by transmitted light. This is 
due to a scattering of the light caused by repeated reflections 
from one particle to another of the suspended substances which 
causes the cloudiness of the water and it is obvious that this 
scattering of light must lead to a reduction in the intensity of 
the light that passes through the cloudy medium. This ex- 
plains why lamplight and sunlight lose so much of their inten- 
sity during time of fog. 

It is necessary to point out that very much depends upon 
the size of the particles of the cloudy medium, as to the degree 
of action upon the light which falls upon it, or is transmitted 
through it. If they are small, they have the effect described 
above; but if large, they have very little selective effect. 
Thus it is that under certain conditions of fog and mist, the 
only effect is to reduce the intensity of the sunlight, but not 
to alter the quality of its colour ; thus also it is that some- 
times the light reflected from the clouds appears to be white, 
while at others it appears to have a bluish or pinkish hue, due to 
variations in the size of the particles of water of which they 
are composed. * 



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COLOUK IN DECQKATION AND DESIGN. 139 

(2) Illumination by artificial light. Artificial lights — gas 
in its various forms, oil, and the electric light — play such an 
important part in illumination that it is important to consider 
their effect upon the colour of objects, etc. It has been shown 
in a previous section what effect coloured light has when it 
falls upon other colour)^. Now, in the case of most of the arti- 
ficial lights, the light emitted is not pure white, but is usually 
more or less tinted, the prevailing hue being yellow in the ordin- 
ary flame of gas, oil and the incandescent electric light ; therefore 
the effects are the same as those which have been shown to 
occur when yellow light falls upon colours. It is a well-known 
fact that there are many colours which perceptibly change in 
hue when exposed to artificial light. Some of the blue and 
green dyes which the textile colourist uses are thus affected — 
blues especially are altered, so that it is often impossible to see by 
night whether a particular shade of dyed cloth is actually 
green or blue. Blacks which by daylight are bluish in tone 
show a dead black under gaslight. Blues tend to become 
greenish, and hence in designing, where the object is to be 
shown under artificial light, it is necessary to employ a blue of 
a reddish hue rather than a blue of a greenish tint. The pig- 
ment smalts changes colour in a similar manner. The ame- 
thyst, which is a pale violet by day, becomes redder at night> 
The sapphire, which is blue by day, exhibits a violet tint by 
night. Some flowers of a blue colour show a reddish tint by 
gaslight. All these effects are due to the deficiency of the or- 
dinary artificial light in the blue and violet rays, therefore the 
objects illuminated appear to be richer in red and yellow than 
they really are. In many cases, to make an object appear to- 
be perfectly white, and to counteract a slight yellow tint that 
it shows, it is given a bluish tint. This is more particularly 
shown in the bleaching of textile fabrics, where the bleached 
fabric has a perceptibly yellow tint. To avoid this effect it is 
customary to pass the fabric through a liquor containing a 



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140 THE THEORY OF COLOUR. 

asmall quantity of blue dye-stuff; the slight amount of bluing 
that is thereby given neutralises the yellow effect, and the 
fabric appears white in daylight. In gaslight, however, the 
effect of this is not appreciable, and the fabric loses its 
brilliant appearance, becoming more or less dull looking. 

The third condition of illumination bf objects is that when 
:seen under a dominant coloured light, which has a very 
material effect upon them. Reference may be made to a pre- 
vious section, in which the effect of one coloured light falling 
upon another has been discussed in some detail. One may 
•conveniently observe these effects by looking at a landscape 
through various coloured glasses, if, for example, a piece of 
yellow glass be used it will be noticed that, while all yellow 
portions are intensified, but are otherwise unchanged, the red 
objects tend to acquire an orange cast, blue objects^become a 
.greyish-green colour, and green objects a yellowish-green 
•colour, and so oh. In many cases the effects obtained are 
considerable ; thus, by viewing a landscape through variously 
tinted glasses, one may produce the changes in appearance 
<iue to various seasons. It may be pointed out, however, that 
the effects observed by viewing objects through a coloured glass 
are nob the same as viewing them under coloured artificial light, 
because all objects illuminated by daylight reflect some white 
light, and this white light modifies the effect as seen through 
the coloured glass. On the other hand, when an object is il- 
luminated by a dominant coloured light — such as, for instance, 
that which is obtained from gas or electric light enclosed in a 
coloured globe — no white light is reflected from them and they 
appear much darker. 

We come now to the fourth case — that is, illumination by 
two lights of different qualities and intensities. This double 
illumination, producing striking effects, is met with very 
frequently in nature, especially at night, for example, in black- 
smiths' forges, street illumination, and in the case of confla- 



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COLOUR IN DECORATION AND DESIGN. 141 

grationa It is very diflBcult to lay down any laws governing 
double illumination, so much depends upon the kind and 
relative degree of the two sources of light. A very simple- 
experiment in this connexion may be carried out in the follow- 
ing manner : — 

Place a screen formed of a sheet of white paper or white 
cloth in such a position that it will be illuminated by daylight 
and by candle-light at the same time ; then place in position a- 
rod so that a shadow is projected by each light on the paper. 
It will now be observed that the shadow produced by the day- 
light will be tinged yellow, while that from the candle will be 
tinged blue ; these effects are, of course, produced by the dif- 
ferent qualities of the two sources of light. The candle-light 
is deficient in blue rays, while the sunlight is proportionately- 
rich in such rays. Now the ^shadow thrown by the candle is- 
illuminated by the sunlight, and in consequence appears bluish, 
because all the surrounding parts of the screen being illuminated 
by both sources of light, the yeUow rays preponderate, and by 
contrast we have a blue effect of the shadow; on the other 
hand, the shadow caused by the daylight is illuminated by the 
yellow rays of the candle-light, and in contrast to the illumin- 
ated screen appears of a yellowish tint. Very curious effects, 
of this character are often observed in churches or chapels 
having stained glass windows. In such places objects are often 
illuminated and shadows cast by two sources of illumination 
— the white light from some windows, the coloured light from* 
others ; the contrasts thus produced are extremely interesting. 
In hilly districts, at the periods of sunset and sunrise, especially 
in the former case, one often gets similar peculiar effects of 
double illumination, inasmuch as the ground and the objects, 
especially of distant hills behind which the sun is either setting 
or rising, ar^ often illuminated by the sun's rays, and at the 
ss^me time by the illumination from the blue sky, this double 
illumination having results upon the surrounding objects. 



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142 THE THEORY OF COLOUR. 

which are more readily observed than described. Artists, 
particularly, are apt to observe the contrast effects produced 
by double illumination, and are able to produce some very 
beautiful pictures by copying them as closely as possible. 

All objects visible to the eye are perceptible because of the 
light which they reflect, as stated in previous sections of this 
book. The cause of colour in coloured objects has also been 
pointed out. In addition to the reflecting action of a sub- 
stance on light, the structure of the surface has to be taken 
into consideration, inasmuch as it very materially affects the 
intensity or beauty of the colour that an object may have. 
This may be noticed in the different appearance that the same 
dj^e-stuff imparts to different textile fabrics ; thus on silk a 
colour is much more brilliant than it is on wool or cotton. 
Again, the structure of a textile fabric has a very material 
influence upon the appearance of a colour. A colour is much 
richer when it is dyed upon a piece of silk velvet that when it 
is dyed upon a piece of plain silk ; hence it is evident that 
texture of surface has a modifying influence on the appearance 
of the colour, and we have now to consider some of the causes 
which bring this about. 

All objects, whether coloured or colourless, reflect some 
white light — even the most intense black surfaces reflecting 
from 3 to 4 per cent, of white light. Now, this white light 
which is reflected has considerable influence upon the colour 
which an object may have; generally its effect is to lessen its 
intensity. One may perhaps notice this point more particularly 
with metals than with other objects. Metals have considerable 
power, when they are bright and untarnished, of reflecting 
light — the greater the amount of light they reflect, the less 
colour they appear to have. Owing to tarnishing or other 
causes the power of reflecting becomes diminished, then the 
metals have a stronger colour. Again, a great deal depends 
upon the manner in which light is reflected from metallic 



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COLOUR IN DECORATION AND DESIGN. 143 

surfaces, and also upon the angle at which the metal is viewed. 
If it is viewed in such a manner that the light skims the sur- 
face of the metal — as when we look along a highly polished 
plate of gold — the metal may appear to be almost white; but 
if we look at it at a smaller angle, then the colour of the metal 
begins to show itself; while, if a couple of plates of metal be 
placed parallel to one another, then the light which is reflected 
from surface to surface becomes more affected, and we get a 
strong development of the colour of the metal — gold under 
such conditions acquiring a very deep orange colour. It is 
owing to these repeated reflections that chased or frosted gold 
has a much richer colour than burnished gold; and for the 
same reason in metallic vessels which are highly polished, the 
interiors appear of a much greater brilliancy than the 
exteriors, on account of the light suft'ering repeated reflections 
from side to side. It may be pointed out that the quality of 
the light is altered by this repeated reflection ; certain rays 
are absorbed more and more, while the total amount of light 
reflected from the surface is less. 

The influence of surface structure is also seen, in painting, 
the difierence which exists in the appearance of the same pig- 
ments when used in water-colour drawing, or in fresco painting, 
or in oil-painting being very mat*ked : in oil-paintings the 
surface being more transparent and homogeneous, the colours 
have a more intense and brilliant appearance; while in water- 
colour paintings the surface is more opaque,^ and the colours 
appear by no means so intense. The greater amount of white 
light which is reflected from a water-colour drawing than from 
an oil-painting brings about this reduction in the intensity of 
the colours. 

A similar influence may be noted in regard to pottery and 
porcelain: colours have a brilliancy and intensity on glazed 
porcelain which they do not show on unglazed porcelain, this 
being due to the greater amount of light which penetrates into 



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144 THE THEOBY OF COLOUE. 

the body of the porcelain, the light which emerges is thus raore 
saturated with colour. 

Colour plays a very important part in the decoration of 
textile fabrics; it is, however, materially influenced by the 
character of the fibre on which it is applied. The colour of 
textile fibres is produced partly by reflection and partly by 
*^ absorption. When light falls upon the coloured fabric a small 
portion is reflected as white light, a somewhat larger portion 
as coloured light, the latter passes into the fibre, and the 
colouring matter on the fibre exerts an absorptive effect on this 
light, causing it to become coloured : it is this portion of the 
light that ultimately makes most impression on the eye. When 
one is looking at a single piece of coloured yarn, or a very thin 
piece of cloth, the intensity of the colour appears slight, it- 
appears poor and weak ; if, however, there are a number of 
threads or a number of folds of cloth, then the colour appears 
more intense and strong. 

The various textile fibres differ from each other with 
regard to lustre, which depends upon their structure and 
power of reflecting light. Lustre has a material and bene- 
ficial influence on the appearance of dyed fabrics — a fact well 
known to dyers, who endeavour to enhance the beauty of the 
colours they produce by imparting a lustre to their gcods. 

Silk is the most lustrous of the textile fibres ; wool ranks 
next, followed by China grass, cotton, linen, jute and hemp,, 
in the order given. Silk owes its lustre to several causes: it 
is homogeneous in structure, is somewhat transparent, its 
outer surface is smooth, and is thus capable of reflecting 
light in definite directions; therefore more reflected light 
reaches the eye from silk than from wool, while the length 
of the silk fibre, with its smooth structure, allows the fibres 
to be laid more parallel to one another in throwing and 
weaving than is the case with any other fibre, thus increasing 
the reflective power of silk fabrics. 



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Plate XI. 




(Theory of Colour). 



Colour Contrasts. 



To face p, 144. 



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COLOUR IN DECORATION AND DESIGN. 145 

Wool comes next in its degree of lustre, but as its sur- 
face is rougher than that of silk, it does not reflect so 
much light, and this is more scattered than is the case with 
silk. 

China grass may take rank next to wool in lustre. Its 
fibres are long and parallel in formation — a fact which goes 
a long way to explain its having greater lustre than cotton. 
The cotton fibre does not possess much lustre. This is due 
to its short length and its twisted character, which causes it 
to scatter the light- falling upon it and not to reflect it in a 
definite direction. 

Linen, jute and hemp have practically no lustre. They 
^ are fibres not homogeneous in structure, and ai'e also some- 
wha.t rough, consequently their power of reflecting light i^ 
but small. 

The effect of lustre upon the colour of dyed fabrics may 
be observed by dyeing the various fibres with a single dye- 
stuff* and then comparing the results. It will be observed 
that the colour looks more brilliant on silk than it does on 
wool, and more brilliant on cotton than on linen or jute. 
The character of the fabric has also a material influence on 
the appearance of the colours dyed upon it. Thus a smooth 
fabric never has so .solid an appearance as a fabric with a 
raised surface. This is strikingly shown by comparing the 
front and back of a piece of velvet, or a piece of plain black 
silk, with a black velvet dyed in the same way and from the 
same materials. The velvet has a much more solid and rich 
appearance. This is due to the fact that the pile of velvet, 
being presented to the light, allows it to penetrate into the 
fabric and be more completely saturated with colour before 
' being reflected to the eye, while the ends of the fibres forming 
the nap or pile reflect but little white light, and therefore the 
light from the substance of the pile is not interfered with. 

Silk velvet is richer in appearance than cotton velvet, because 

10 



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146 THE THEOKY OF COLOUE. 

of the greater direct reflective power of the fibre, cotton 
scattering the light more. 

The loose fibrous structure of dyed woollen cloth causes 
it to have a greater appearance of solidity than has dyed 
cotton cloth, or even worsted cloth, wherein the fibres are 
kept cldser together. Dyed cotton flannelettes, for the same 
reason, have a better appearance as regards depth of colour 
than have plain cotton cloths. 



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CHAPTER VII. ^"''' 

MEASUREMENT OF COLOUR. 

The practical colourist has often to test or examine the 
colouring matters he uses for their actual tone or strength, 
^nd a description of the methods in common use for this 
particular purpose will be useful. It may be stated, however, 
that we shall not concern ourselves with the methods of 
testing those properties of colouring matters upon which their 
application in the various arts of painting, dyeing, etc., 
depends. The consideration of such properties will be found 
in books relating to the special subjects, such as the author's 
Manual of Painters* Colours and Knecht and Rawson's 
Manual of Dyeing, to which we refer the reader. What we 
describe here are the methods for estimating the tone and 
strength of colouring matters of various kinds. 

ABNEY'S COLOUR PATCH PROCESS. 

Captain Abney some years ago described a new form of 
apparatus for the measurement of colour, which he called a 
" colour patch apparatus," this will be found described and 
illustrated in his book on Colour Measurement and Mixture. 
With this apparatus it is quite possible to measure the tone 
and value of any colouring matter. 

The apparatus may be described as follows : The source of 
the light used is an electric arc lamp, which Captain Abney 
selected because it was found to be a more regular source of 
light than any other which was tried. The light from this 

(147) • 



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148 THE THEORY OF COLOUR. 

arc is allowed to fall upon the coUimating lens of a spectro^ 
scope, and from thence passes through the prisms of the instru- 
ment, into a photographic camera, on the focussing screen of 
which it is received as a spectrum. As the reflective powers, 
of the diflerent colours vary they are not all brought to at 
focus on the same plane, therefore to allow for this the focus- 
sing screen is placed slightly oblique so as to get as near a. 
focus for all the rays as possible. At a distance of about four 
feet from the camera is placed a white screen, on which the: 
rays can be received after passing through the camera. When 
the focussing screen is removed the rays form a confused! 
mass of coloured light; by interposing a lens this mass of 
light can be resolved into a patch of white light. If, how- 
ever, a card containing a vertical slit be put in place of the: 
focussing screen, there will be obtained a patch of colouredl 
light upon the screen, the colour depending upon the posi- 
tion of the card in the camera ; by moving this card to and 
fro there may be obtained upon the screen any portion of the 
spectrum which may be desired. By taking advantage of 
the fact that the front face of the prism reflects a portion of 
the light which falls upon it from the coUimating lens of the 
spectroscope, passing this light through a lens of suitable- 
focus, and then reflecting it from a' small mirror on to the 
screen, it is possible to obtain two patches of white light from 
the same source, and therefore practically equal in value in 
every respect. By placing a rod in front of the screen, which 
can be illuminated both by the light that has passed through 
the spectroscope and by the light which is reflected from the 
mirror, we have the means of comparing the twoi lights in a 
very correct manner. If their intensities are equal, then the 
shadows cast by the rod will also be equal in intensity ; if 
one be stronger than the other, then the shadows will difler 
also ; by employing an instrument with a pair of revolving^ 
sectors, and placing these in the path of either of the beams 



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MEASUEEMENT OF COLOUE. 



149 



of light, its intensity may be reduced to any required de- 
gree. 

The instrument just referred to consists of an electro- 
motor /carrying on its spindle a pair of fast and a pair of 
loose sectors. The latter are so contrived that during their 
rotation the aperture they form with the fixed sectors can be 







Fig. 70. 

varied to any required degree, so that the amount of light 
which is aUowed to pass through these apertures may be 
altered as required. The arrangement of the apparatus is 
shown in the diagram Fig. 70. 

This apparatus can be used for the measurement of colour 
in the following manner : The screen is replaced by a revolv- 
ing disc arrangement such as shown in Fig. 44 ; this revolving 



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150 



THE THEOKY OF COLOUR. 



arrangement carries in the centre a disc painted with the 
pigment which it is desired to examine ; then black and 
white discs are so arranged that the proportion of black to- 
white may be proportioned as required. The apparatus is 
arranged so that a patch of light from one portion of the 
spectrum falls upon the screen in such a manner that it 
illuminates both the centre coloured disc and the black and 
white sectors ; by moving the slit along the spectrum the hue 




Fig. 71. 

of the central disc may be matched, while its luminosity is 
measured by altering the proportions of the black and white 
sectors. In this way the exact hue of the colour may be 
valued, and by passing the slit along the spectrum the 
amount and character of the rays which are reflected by the 
pigment can be ascertained by laying down on a diagram the 
values or the position in the spectrum, and the relative 
luminosity of the light, and a curve can be drawn as in Figs. 
20, 21, et seq. ; further, it is possible to make a template of a 



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MEASUREMENT OF COLOUR. 151 

colour which, when placed in the rotating apparatus and 
rotated in front of the colour patch of the spectrum produced 
by the spectroscope on the screen, will reproduce exactly the 
hue of the colour. This is done by drawing a part of an 
arc, laying out along one of the radii the relative positions of 
the various rays of the spectrum, and from these points 
drawing concentric circles along wliich the relative lumin- 
osities are laid down ; by cutting out the curve so formed, 
a template is made which, when rotated as described, matches 
the colour. Such a template is shown in Fig. 71, which is 
reproduced from Captain Abney's book. 

This method of measurement is applicable only to colour- 
ing matters in the form of pigments, or which may be spread 
upon the surface of a card or other medium. 

THE TINTOMETER. 

A very convenient apparatus, which may be applied to 
the measurement of a great variety of coloured substances, is 
the instrument invented by Mr. J. W. Lovibond of Salisbury, 
and named by him the tintometer. The essential part of this 
instrument consists of a box, rectangular in section, broad at 
one end and tapering to the other, in which an eyepiece is . 
placed ; down the centre of the box is a partition dividing the 
instrument into two parts. If light is passed along the two 
tubes only one field of view is presented to the eye ; if now 
there is interposed in one side of the apparatus a coloured 
substance, the field of view of that half will be coloured, while 
the other half remains white. If in the second half of the 
apparatus another coloured substance be inserted, we have 
the means of comparing exactly the colours of the two pro- 
ducts in question ; if the second coloured body is of a standard 
character, we have a means of comparing the first in terms of 
the second and also of keeping a record of the observation. 

A number of coloured glasses of various hues graduated in 



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152 THE THEOBY OF COLOUR. 

intensity are supplied with the instrument, these glasses being 
standardised and numbered. They are placed in slots pro- 
vided on the one side of the apparatus while the material to 
be examined is placed on the other. By selecting the glasses 
it is possible to match any colour. 

The tintometer may be used for almost any substance. 
Thus, suppose thatthe hue and depth of tint of a pigment are 
to be determined. The pigment may be fiUed into a flat box 
with a glass lid which is put on one side of the apparatus ; a 
similar box filled with precipitated calcium sulphate being 
placed on the other ; on taking an observation the colour 
of the pigment will be visible on the one side of the lens and 
white on the other. Coloured glasses are now put in one by 
one until the hue of the pigment is exactly matched, when the 
colours and the numbers are read off. For dull tones and 
neutral tints, smoke-grey and brown colours are provided, in 
addition to the pure colours. 

When coloured solutions are ^ to be examined these are 
placed in a narrow trough of a definite length with glass front 
and back, the matching of the colour following the same lines 
as that for pigments. Ground glasses of several degrees of 
opacity are provided for turbid liquids. 

The tintometer can be used to measure the colour of all 
kinds of coloured substances and is the most practical and 
convenient apparatus for the purpose that has been devised. 
For a fuller description the reader is referred to Mr. J. W. 
Lovibond's Measurement of Light and Colour Sensations, 

For the purpose of measuring tints of coloured bodies 
various other instruments have been invented from time to 
time. In Fig. 72 is shown the chromometer designed by Mr. 
Wilson for measuring the colour of petroleum oils, but which 
may be used for other colorimetric determinations with 
liquids. This instrument consists of two small tubes closed 
at each end by a screw cap carrying a stout glass disc : light 



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MEASUREMENT OF COLOUR. 



153 



is reflected upwards through the tubes by means of a mirror, 
and is then, by means of prisms, refracted and brought into 
the eyepiece ; one of the tubes is filled with the oil to be 
tested, and in the other, which is empty, a disc of tinted glass. 
On looking through the eyepiece the field of view is seen to be 
divided by a sharp line formed at the junction of the two 
images produced by the prisms, one half of the field being 
tinted with the colour of the oil, the other half with that of 




Fig. 72. 



the standard. An accurate comparison can then be made of 
the quality of the oil as regards colour. For the purpose of 
testing petroleum oil the instrument is supplied with a set 
of four standard glasses, representing the grades of colour of 
xjommercial petroleum oil which are recognised. 

This instrument may also be employed for measuring 
^comparative intensities, by filling the two tubes with the oils 
that are to be compared, and viewing them through the eye- 
piece. 

Other similar forms of colorimeters have been devised by 



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154 THE THEORY OF COLOUR. 

Ridsdale and others, which, however, do not need detailed 
description here. 

For examination of the comparative strengths of dyes or 
coloured solutions this apparatus may be used in the f oUowing^ 
manner : A solution of a known quantity of a standard colour 
in a measured quantity of water is made ; then a solution of 
the colour to be tested is also made of the same strength ; a 
measured quantity of the standard solution is placed in one 
of the tubes, and the same quantity of the other solution in 
the second tube. An observation is now made by looking 
down the tubes, as to whether both exhibit the same inten- 
sity of colour; if one be lighter than the other, then the 
quantity of the solution is added to until a new observation 
shows that both have exactly the same depth of tint. Then 
the volumes of the two liquids may be taken as measurements 
of the comparative strength of the two colouring matters. 

When a colorimeter is not available, a comparison of 
two colours, such as two dye-stufls which are soluble in 
water, may be made by taking a weighed quantity, say^ 
one gramme, and dissolving in 100 cc. of water. Next two 
tubes with flat bottoms and of the same diameter and a 
capacity of about 80 cc. are procured ; the diameter of these 
need not be more than f inch. Measure into each glass 30 cc. 
of water and 10 cc. of the dye solution, then hold the glasses 
in an inclined position over a white card and compare the 
colour of the two solutions for depth. To the strongest add 
water until the depth of colour in both glasses is identical ; 
then measure the length of each column of liquid, this mea- 
surement will give the comparative value of the colouring 
power of the two substances. 

In the case of pigments the relative colouring value of two- 
samples may be determined in the following manner : — 

By comparison with standard sample. Supposing the 
colouring power of a sample of vermilionette is to be deter- 



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MEASUREMENT OF COLOUR. 155 

mined, then 10 grammes of the, sample are weighed out and 
mixed with 30 grammes of china clay; the mixing being 
thoroughly done. Ten grammes of the standard sample are 
mixed in the same way with 30 grammes of the same sample 
of china clay. The two mixtures are now spread on paper in 
equal thicknesses compared together for depth of colour as 
described above : if the two samples are equal in colouring 
power, the depth of colour of the two mixtures will be the 
same; if one is stronger than the other, then one of the 
. mixtures will be darker than the other. Some idea of the 
relative strength of colouring power can be obtained by adding 
small and known weights of ehina clay to the darkest sample, 
until the tint of the mixtures is equal ; then the samples have 
a colouring power proportional to the amount of china clay 
used. Thus, if one sample took 30 grammes of china clay 
and the other sample 37*5 grammes, then the relative colour-, 
ing power is as 30 to 37*5; or, if the strongest sample be 
taken as 100, then the colouring power may be expressed in 
percentages thus — 37*5 : 30 : : 100 : 80 ; the weakest colour 
having only 80 per cent, of the colouring power of the 
strongest. 

Again, in making some experiments to test the comparative 
colouring powers of Orr*s white and white lead, 5 grammes 
of the former were mixed with 1*46 grammes of blue, and 
the tint thus formed was found to be exactly matched by a 
mixture of 5 grammes of white lead with 0*55 gramme of 
blue. Hence we have : — 

146 : 55 : : 100 = 2366, 

that is, 100 parts of Orr's white is equal to 236*6 parts of 
white lead as regards colouring power. These proportions 
are, of course, by weight ; as white lead is much heavier than 
Orr's white it naturally occupies less bulk and requires less. 
colour to affect it. 



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156 THE THEORY OF COLOUR. 

As the toning colour for all pigments, except whites, a 
good sample of china clay may be used ; gypsum may also 
he used ; barytes and white lead are a little too heavy. For 
"whites a good animal black serves as a toning colour. 

When a large number of assays for colouring power have 
■to be made, a standard tint should be prepared by taking, say, 
50 grammes of the standard sample, and mixing with about 
twice its weight of the toning colour ; this tint may be used 
in subsequent tests, and will save time in the preparation of 
•a standard tint. It is important, however, that the same 
•isample of toning colour be used to mix with the samples 
ivhose colouring power is being tested, as that used in making 
the standard tint. 



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INDEX. 



Abney's colour patch apparatus, 

147. 
Absorption spectra, 33. 

— — of colouring matters, 

38. 

— spectrum of acid green, 40. 

— — of alizarine, 43. 

— — of aniline blue, 40. 

— — of Bismarck brown, 43. 
_ _ of blue glass, 37. 

— — of cadmium yellow, 48. 

— — of carmine, 45. 

— — of chlorophyll, 51. 

— — of chrome green, 46. 

— — of chrome yellow, 48. 

— — of cochineal, 43. 

— — of cyanol, 40. 

— — of dragon's blood, 42. 

— — of emerald green, 46. 

— — of eosine, 40. 

— — of green glass, 37. 

— — of Indian red, 46. 

— — of indigo extract, 40. 

— — of iodine green, 41. 

— — of magenta, 39. 

— — of methyl violet, 40. 

— ~ of naphthaline red, 42. 

— — of orange glass, 36. 

— — of picric acid, 39. 

— — of Prussian blue, 60. 

— — of purpurine, 43. 

— — of red glass, 34, 35. 

— — of rhodamine, 40. 

— — of safranine, 39. 

— — of scarlet R, 39. 

— — of smalt, 49. 

— — of tartrazine, 39. 

— — of terra verte, 47. 

— — of turmeric, 42. 

— — of ultramarine, 49. 



Absorption spectrum of ultra- 
marine green, 49. 

— — of vermilion, 45. 

— — of yellow ochre, 48. 
Acid green, absorption spectrum. 

of, 40. 
Action of prism on light, 2. 
Alizarine, absorption spectrum of,. 

43. 
Aniline blue, absorption spectrum 

of, 40. 
Artificial lights and colours, 139. 

B. 

Bismarck brown, absorption spec- 
trum of, 43. 

Blue glass, absorption spectrum 
of, 37. 

— light on colours, 66. 
Brewster theory of colours, 55, 79. 
Browning's direct vision spectro- 
scope, 10. 

C. 

Cadmium yellow, absorption 

spectrum of, 48. 
Carmine, absorption spectrum of,, 

45. 
ChevreuTs laws of harmonious 

contrast, 128. 
Chlorophyll, absorption spectrum 

of, 51. 
Chromatic aberration, 128. 

— circle, 110. 

Chrome green, absorption spec- 
trum of, 46. 

— yellow, absorption spec- 

trum of, 48. 
Chromometer, 152. 
Cochineal, absorption spectrum 
of, 43. 



(157) 



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158 



THE THEORY OF COLOUR. 



Colour and coloured lights, 136. 

— — coloured bodies, 32. 

— — gaslight, 136. 

— — illumination, 136. 

— - light, 1. 

— — polarised light, 23. 

— — sunlight, 136. 

— — textile fabrics, 144. 

— blindness, 102. 

— by the polariscope, 19. 

— combinations, 61. 

— — harmony of, 125. 

— — laws of, 128. 

— contrast in decorative de- 

sign, 117. 

— contrast, Ragona Scina's 

apparatus, 111. 

— equivalents, 75, 127. 

— in decoration and design, 

123. 
-'■ measurement, 147. 

— — by tintometer, 151. 

— nerves, 93. 

— — sensitiveness, 98. 

— pairs, 109. 

— phenomena and theories, 

55. 

— — subjective, 96. 

— photography, 83. 

— shades, 74." 

— spaces in normal spectrum, 

— theories, 79. 

— theory, Brewster's, 55, 79. 

— — He ring's, 90. 

— — Maxwell's, 82. 

— — Young-Helmholtz's, 79. 

— tints, 74. 

Coloured bodies and light, 32. 

— designs, harmony of, 130. 

— light and colour, 136. 

— lights, combining, 58. 

— — mixing, 62. 

— spaces in spectrum, 5. 
Colouring matters, absorption 

spectra of, 38. 
Colours and artificial lights, 136. 

— and pottery, 143. 

— on coloured grounds, 118. 

— complementary, 64, 75. 

— contrast of, 105, 108. 

— fluorescent, 26. 

— hue of, 13. 

— interference, 27. 



j Colours, luminosity of, 14. 
I — mixing, 67. 
j — phosphorescent, 26. 
I — primary, 72, 80. 
■ — produced bv mixing dyes, 
41-43. 

— purity of, 18. 

— secondary, 72, 80. 

— spectrum, 2. 

— successive contrast of, 113. 

— supplementary, 79. 

— tertiary, 72. 

— transmitted, 32. 
Combining coloured lights, 58. 

— colours, 58. 
Complementary colours, 64, 75. 
Contrast, 105. 

— of colour, 108. 

— of colours, 105. 

— harmonies of, 125, 132. 

— of tone, 105. 

— simultaneous, 105. 

— successive, 105, 113. 

— theories of, 120. 

Cyanol, absorption spectrum of, 
40. 



Decoration and design, colour in, 
117, 123. 

Decorative design, colour con- 
trast in, 117. 

Diffraction grating, 8. 

Dispersion of light by prism, 2. 
— of white light, 2. 

Dove's dichroiscope, 59. 

Dragon's blood, absorption spec- 
trum of, 42. 

Dyestuffs, mixing, 69. 



Electric rotatory apparatus, 56. 

Emerald green, absorption spec- 
trum of, 46. 

Eosine, absorption spectrum of, 
40. 

Eye, 91. 

— as an optical instrument, 

100. 

— structure of the, 91. 



Digitized by VjOOQIC 



INDEX. 



159 



Fixed lines, solar spectrum, 4. 
Fluorescence, 26. 
Fluorescent colours, 26. 
Frauenhofer lines, 4. 
Fresco drawing, 63. 

Q. 

Gaslight and colour, 136. 
Green light on colours, 66. 

— glass, absorption spectrum 
of, 37. 

H. 

Harmonies of analogy, 131. 

— of contrast, 132. 
Harmonious contrast of colours, 

128. 
Harmony of colour change, 133. 

— of colour combinations, 125. 

— of coloured designs, 130. 

— of scale, 131. 

— of succession, 133. 
Helmholtz's theory of colour, 80. 
Bering's theory of colour, 90. 
Hue, 13. 



I. 



Illumination and colour, 136. 

Indian red, absorption spectrum 
of, 46. 

Indigo extract, absorption spec- 
trum of, 40. 

Influence of coloured light on 
colours, 65. 

— of medium on colours, 62. 

— of surface on colours, 62. 
Interference colours, 27. 

Iodine green, absorption spectrum 
of, 41. 



K. 



Kromskop, 86. 



Laws of harmony, 128. 
Light, 1. 

— and colour, 1. 

— polarised, 20. 



Light wave, motion of, 7. 
— waves, lengths of, 8. 
Lovibond's tintometer, 161. 
Luminosity of colours, 14. . 
Luminous bodies, 1. 



Magenta, absorption spectrum of, 

39. 
Maxwell disc experiments, 67. 

— discs, 68. 

— theory of colour, 83. 
Measurement of colour, 147. 
Methyl violet, absorption spec- 
trum of, 40. 

Mixing coloured lights, 62. 

— colours, 56, 67. 

— dyestufifs, 69. 

— spectral colours and white 
light, 18. 

N. 

Names of colours, 3. 
Naphthaline red, absorption spec- 
trum of, 42. 
Nerve fibres and colour, 94. 
Newton's colour disc, 13, 66. 

— experiment, 2. 
Nicol's prism, 20. 
Normal spectrum, 9. 



Orange glass, absorption spec- 
trum of, 36. 

P. 

Persistence of vision, 93. 
Phosphorescence, 26. 
Phosphorescent colours, 26. 
Photo-chromoscope, 85. 
Photography, colour, 83. 
Physiology of light, 91. 
Picric acid, absorption spectrum 

of, 39. 
Pigments, testing, 164. 
Polariscope, 20. 
Polarised light, 20. 

— — and colour, 19, 23. 
, — — and crystals, 23. 
Pottery and colours, 143. 



Digitized by VjOOQIC 



160 



THE THEORY OF COLOUR. 



Primary colours, 72, 80. 
— . — and white light, 81. 

Producing a spectrum, 3. 

Prussian blue, absorption spec- 
trum of, 50. 

Purity of colours, 17. 

Purpurine, absorption spectrum 
of, 43. 

B. 

Kagona Scina's colour apparatus, 

111. 
Recomposition of white light, 11. 
Red glass, absorption spectrum 

of, 34, 36. 

— light on colours, 66. 
Retina of eye, 92. 
Rhodamine, absorption spectrum 

of, 40. 
Rothe's rotary apparatus, 57. 

S. 

Safranine, absorption spectrum 
of, 39. 

Scarlet R, absorption spectrum 
of, 39. 

Secondary colours, 72, 80. 

Separation of colours in design- 
ing, 129. 

Simultaneous contrast, 105. 

Smalt, absorption spectrum of, 49. 

Solar spectrum, lines in, 4. 

Spectroscope, 10. 

Spectrum, 2. 

— colours, 2, 15. 

— — names of, 3, 4. 

— — relative space of, 6, 9. 

— lines, 4. 

— normal, 8. 

— producing a, 3. 
Subjective colour phenomena, 96. 
Successive contrast, 105. 

— — of colours, 115. 
Sunlight and colour, 136. 
Supplementary colours, 79.. 
Surface and colour, 52. 



Tartrazine, absorption spectrum 

of, 39. 
Terra verte, absorption spectrum 

of, 47. 
Tertiary colours, 72.* 
Textile fabrics and colours, 144. 
Theories of contrast, 120. 
Tintometer, 151. 
Transmitted colours, 32. 
Turmeric absorption spectrum 

of, 42. 

U. 

Ultramarine, absorption spectrum 
of, 49. 
— green, absorption spectrum 
of, 49. 



Vermilion, absorption spectrum 

of, 45. 
Vision, persistence of, 93. 

W. 

Wave lengths of light, 8. 

— — of colour^, 14. 

— motion of light, 7. 
White from coloured lights, 65. 

— light, recomposition of, 11. 

— — dispersion of, 2. 
Wilson's chromometer, 151. 



Yellow light on colours, 65. 
, — ochre, absorption spectrum 

of, 48. 
Young-Helmholtz theory of 

colours, 80. 

Z. 

Zollner's lines, 100. 



ABERDEEN: THE UNIVERSITY PRESS. 



Digitized by VjOOQIC 



Hfirlbaeb Catalogue 

OF 

Special Weednieal Sdooks. 



INDEX TO SUBJECTS. 



PAGE 

Adhesives 10 


PAGB 

Engineering Handbooks 19, 20 | 


Agricultural Chemistry .. 


9 


Engraving 


. 24 


Air, Industrial Use of ... 


10 


Essential Oils 


.. 7 


Alcohol, Industrial 


9 


Evaporating Apparatus . 
External Plumbing 


.. 18 


Alum and its Sulphates .. 


8 


.. 21 


Ammonia 


8 


Fats ... 


.. 6 


Aniline Colours 


3 


Faults in Woollen Goods 15 1 


Animal Fats 


6 


Flax Spinning 


.. 17 


Anti-corrosive Paints 


4 


Food and Drugs ... 


.. 23 


Architecture, Terms in .. 


22 


Fruit Preserving ... 


.. 23 


Architectural Pottery .. 


12 


Gas Firing 


.. 18 


Artificial Perfumes 


7 


Glass-making Recipes 


.. 13 


Balsams 


9 


Glass Painting 


.. 13 


Bleaching Agents, etc. .. 


17 


Glue-makmg and Testing. 


.. 8 


Bone Products 


8 


Glycerine 


.. 7 


Bookbinding 


24 


Greases 


.. 6 


Brick-making ... 11 
Burnishing Brass 


,12 


Gutta Percha 


. 11 


21 


Hat Manufacturing 


.. 15 


Carpet Yam Printing 


16 


Hemp Spinning ... 


.. 17 


Casein 


4 


History of Staffs Potteries 12 ( 


Celluloid 


23 


Hops 


.. 22 


Cement 


22 


Hot-water Supply 


.. 21 


Ceramic Books ... 11 


.12 


India-rubber 


.. 11 


Charcoal 


8 


India-rubber Substitutes 


5 


Chemical Analysis 


8 


Inks 3, 4, 5, 10 1 


Chemical Essays 


8 


Insecticides; etc 


.. 22 


Chemical Reigents 
Chemical Works 


8 


Iron-corrosion 


.. 4 


8 


Iron, Science of ... 


.. 18 


Church Lace 


14 


Japanning 


.. 21 


Clays 


12 


Jute Spinning 


.. 17 


Coal Dust Firing 


18 


Lace*Maktng 


.. 14 


Coal Gas By-Products .. 


9 


Lacquering 


.. 21 


Colliery Reco^rery Work.. 


M 


Lake Pigments ... 


.. 3 


Colour Matcning (Textile) 16 


Lead 


.. 10 


Colour Recipes 


3 


Leather-working Mater'ls 6,1 1 1 


Colour Theory 


16 


Linoleum 


.. 5 


Combing Machines 


17 


Lithographic Inks ... 


5,23 


Condensing Apparatus .. 


. 6 


Lithography 


.. 23 


18 


Lubricants 


.. 6 


Cosmetics 


7 


Manures 


8,9 


Cotton Dyeing 


16 


Meat Preserving ... 


.. 23 


Cotton Spinning 

Cotton Waste 


. 17 


Medicated Soaps ... 


.. 7 


17 


Metal Polishing Soaps . 


.. 7 


Damask Weaving 


15 


Mineral Pigments ... 


.. 3 




22 


Mineral Waxes " ... 


.. 6 


Decorators' Books 


4 


Mine Ventilation ..., 


.. 18 


Decorative Textiles 


15 


Mining, Electricity 


.. 18 


Dental Metallurgy 


18 


Needlework 


.. 14 


Disinfection 


9 


Oil arid Colour Recipes . 


.. 3 


Driers 


5 


Oil Boiling 


.. 5 


Dru^s 


23 


Oil Merchants' Manual . 


.. 6 


Drymg Oils ., 


5 


Oils 5, 6, 7 1 


Drying with Air, etc. 


10 


Ozone, Industrial Use of. 


.. 10 


Dyeing Marble, etc. 


23 


Paint Manufacture 


.. 3 


Dyeing Fabrics 


16 


Paint Materials ... 


.. 3 


Dyers' Materials 


16 


Paint-material Testing . 


.. 4 


Dye-stuffs ... ... .. 


16 


Paint Mixing 
Paper-Mill Chemistry . 


3,4 


Bdible Fats and Oils 


6 


.. 13 


Electric Lamp Develop- 




Pigments 


3,9 


ment 


21 


Plumbers' Books- ... 


.. 21 


Electric Wiring 

Electricity in Collieries .. 


.21 


Pottery Clays 


.. 12 


18 


Pottery Decorating 


.. 11 


Emery 


24 


Pottery Manufacture 11. 12 | 


Enamelling Metal 


13 


Pottery Marks 


.. 12 


Enamels 


13 







PAGE 

Power-loom Weaving ... 14 

Preserved Foods 23 

Printers' Ready Reckoner 24 
Printing Inks ... 3, 4, 5 

Recipes 3, 13 

Resins 9 

Ring Spinning Frame ... 17 
Risks of Occupations ... 10 
Riveting China, etc. ... 12 
Scheele's Essays ... ... 8 

Sealing Waxes 10 

Shale Oils and Tars ... 9 
Sheet Metal Working ... 21 

Shoe Polishes 6 

Silk Dyeing 16 

Silk Throwing, etc. ... 17 

Smoke Prevention 18 

Soap Powders 7 

Soaps 7 

Spinning 15, 17 

Spirit Varnishes 5 

Staining Marble, and Bone 23 
Stain-removing Soaps ... 7 

Standard Cloths 13 

Steam Drymg 10 

Steel Hardening 18 

Sugar Technology ... 24 

Sweetmeats 28 

Tallow 6 

Technical Schools, List ... 24 

Terracotta 12 

Testing Paint Materials ... 4 
Textile Colour Mixing ... 16 

Textile Design 14 

Textile Fabrics ... 13, 14, 15 

Textile Fibres 14 

Textile Materials 14 

Timber 22 

Toilet Soapmaking ... 7 

Varnishes 5 

Vegetable Fats and Oils ... 6 
Vegetable Preserving ... 23 

Warp Sizing 15 

Waste Utilisation 9 

Water, Industrial Use 10, 11 
Water-proofing Fabrics ... 15 

Waxes 6 

Weaving Calculations ... 15 
White Lead and Zinc White 5 
Wiring Calculations ... 21 
Wood Distillation ... 22 

Wood Extracts 22 

Wood Waste Utilisatioo... 22 

Wood-Dyeing 23 

Wool Dyeing 16 

Woollen Goods ... 15, 16 
Worsted Spinning ... 15 

Woven Fabrics 15 

Writing Inks 10 

X-RayWork 11 

Yarn Sizing 15 

Yarn Numbering and Test- 
ing 14,15 

Zinc White Paints ... 5 



PUBLISHED BY 

SCOTT, GREENWOOD & SON 

8 BROADWAY, LUDGATE. LONDON. K.C. (England), 



Digitized by VjOOQIC 



FULL PARTICULARS OF CONTENTS 

Of the Books mentioned In this ABRIDGED CATALOCUE 
will be found in the following Catalogues of 

CURRENT TECHNICAL BOOKS. 



LIST I. 

Artists' Colours — Bone Products — Butter and Msu^rine Manufacture— Casein — 
Cenents— Chemical Works (Designing and Erection)— Chemistry (Agricultural, Indus- 
trial, Practical and Theoretical)— Colour Mixing— Colour Manufacture— Compounding 
Oils— Decorating— Driers— Drying Oils— Drysaltery— Emery— Essential Oils — Fats 
(Animal, Vegetable, Edible) — Gelatines — Glues — Greases — Gums — Inks — Lead — 
Leather — Lubricants — Oils — Oil Crushing — Paints — Paint Mauufacturing — Paint 
Material Testing— Perfumes— Petroleum— Pharmacy— Recipes (Paint, Oil and Colour) 
— Resins— Sealing Wsuces— Shoe Polishes — Soap Manufacture — Solvents — Spirit 
Varnishes — ^Varnishes — White Lead — Workshop Wrinkles. 

LIST II. 

Bleaching — Bookbinding — Carpet Yam Printing— Colour (Matching, Mixing 
Theory)— Cotton Combing Machines— Dyeing (Cotton, Woollen and Silk Goods) — 
Dyers' Materials — Dye-stuffs — Engraving — Flax, Hemp and Jute Spinning and Twisting 
— Gutta-Percha — Hat Manufacturing — Indiarrubber — Inks — Lace-making — Litho- 
graphy—Needlework—Paper Making — Paper-Mill Chemist — Paper-pulp Dyeing — 
Point Lace— Power-loom Weaving— Printing Inks— Silk Throwing— Smoke Preven- 
tion— SoapsT-Spinniiig— Textile (Spinning, Designing, Dyeing. Weaving, Finishing) 
—Textile Materials— Textile Fabrics— Textile Fibres— Textile Oils— Textile Soaps- 
Timber— Water (Industrial Uses) — Water-proofing— Weaving— Writing Inks— Yams 
(Testing, Sizing). 

LIST in. 

Architectural Terms — Brassware (Bronzing, Burnishing, Dipp^g, Lacquering)— 
Brickmaking— Building— Cement Work— Ceramic Industries — China— Coal-dust Firing 
—Colliery Books — Concrete — Condensing Apparatus — Dental Metallurgy— Drainage — 
Drugs— Dyeing — Bsuthenware— Bledtrical Books— Enamelling— Enamels-Engineer- 
ing Handbooks — Evaporating Appsuvtus— Flint Glass-making— Food< — Food Preserv- 
ing-Fruit Preserving— Gas Engines — Gas Firing — Gearing — Glassware (Painting, 
Riveting)— Hops— Iron (Construction, Science) — Japanning— Lead — Meat Preserving 
—Mines (Haulage, Electrical Equipment, Ventilation, Recovery Work from>— Plants 
(Diseases, Fungicides, Insecticides)— Plumbing Books— Pottery (Architectural. Clays 
Decorating, Manufacture, Marks on) — Reinforced Concrete — Riveting (China, 
Earthenware, Glassware) — Sanitary Bngmeering— Steam Turbines — Steel (Hardening, 
Tempering)— Sugar— Sweetmeats— Toothed Gearing— Vegetable Preserving — Wood 
Dyeing— X-Ray Work. 



X:OPIES OF ANY OF THESE LISTS WILL BE SENT 
POST FREE ON APPLICATION. 



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(Paints, Colours, Pigments and 
Printing Inks.) 

THE CHEMISTRY OF PIGMENTS. By Brnbst J. 
Parry, B.Sc. (Lond.), F.I.C., F.C.S., and J. H. Coste, F.I.C, 
F.C.S. Demy 8vo. Five Illustrations. 285 pp. Price lOs. 6d. 
net. (Post free, lis. home ; lis. 4d. abroad.) 

THE MANUFACTURE OF PAINT. A Practical 
Handbook for Paint Manufacturers, Merchants and Painters. 
By J. Cruickshank Smith, B.Sc. Second Edition, Revised and 
Enlarged. DemySvo. 288 pp. 80 Illustrations. Price 10s. 6d. 
net. (Post free, lis. home ; lis. 4d. abroad.) 

DICTIONARY OF CHEMICALS AND RAW 
PRODUCTS USED IN THE MANUFACTURE 
OF PAINTS, COLOURS, VARNISHES AND 
ALLIED PREPARATIONS. By George H. Hurst, 
F.C.S. Demy 8vo. 380 pp. Price 7s. 6d. net. (Post free, 8s. Id. 
home ; 8s. 7d. abroad.) 

THE MANUFACTURE OF LAKE PIGMENTS 
FROM ARTIFICIAL COLOURS. By Francis H. 
Jennison, F.I.C, F.C.S. Sixteen Coloured Plates, showing 
Specimens of Eighty-nine Coioure, specially prepared from 
the Recipes given In the Boole 136 pp. Demy 8vo. Price 
7s. 6d. net. (Post free, 8s. home ; 8s. 2d. abroad.) 

THE MANUFACTURE OF MINERAL AND LAKE 
PIGMENTS. Containing Directions for the Manu- 
facture of aU Artificial, Artists and Painters* Colours, Enamel, 
Soot and Metallic Pigments. A text-book for Manufacturers, 
Merchants, Artists and Painters. By Dr. Josep Bersch. 
Translated by A. C. Wright, M.A. (Oxon.),B.Sc. (Lond.). Forty- 
three Illustrations. 476 pp. Demy 8vo. Price 12s. 6d. net. 
(Post free, 13s. Id. home ; 13s. 7d. abroad.) 

RECIPES FOR THE COLOUR, PAINT, VARNISH, 
OIL, SOAP AND DRYSALTERY TRADES. 

Compiled by An Analytical Chemist. 330 pp. Second Revised 
and Enlarged Edition. Demy 8vo. Price 10s. 6d. net. (Post 
free, lis. Id. home ; lis. 4d. abroad.) 

OIL COLOURS AND PRINTERS' INKS. By Louis 
Edoar And^s. Translated from the German. 215 pp. Crown 
8vo. 56 Illustrations. Price5s.net. (Post free, 5s. 5d. home; 
i>f». 7d. abroad.) 



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MODERN PRINTING INKS. A Practical Handbook 
for Printing Ink Manufacturers and Printers. By Alfred Sey- 
mour. Demy 8vo. Six Illustrations. 90 pages. Price 5s. net. 
(Post free, 5s. 5d. home ; 5s. 7d. abroad.) 

THREE HUNDRED SHADES AND HOW TO MIX 
THEM. For Architects, Painters and Decorators; By 
A. Desaint, Artistic Interior Decorator of Paris. The book con- 
tains 100 folio Plates, measuring 12 in. by 7 in., each Plate con- 
taining specimens of three artistic shades. These shades are all 
numbered, and their composition and particulars for mixing are 
fully given at the beginning of the book. Each Plate is inter- 
leaved with grease-proof paper, and the volume is very artistic- 
ally bound in art and linen with the Shield of the Painters' Guild 
impressed on the cover in gold and silver. Price 21s. net. (Post 
free, 21s. 7d. home ; 22s. 7d. abroad.) 

HOUSE DECORATING AND PAINTING. By W. 

Norman Brown. Eighty-eight Illustrations. 150 pp. Crown 
8vo. Price 3s. 6d. net. (Post free, 3s. lOd. home and abroad.) 

A HISTORY OP DECORATIVE ART. By W. Norman 
Brown. Thirty-nine Illustrations. 96 pp. Crown 8vo. Price 
Is. net. (Post free, Is. 4d. home and abroad.) 

WORKSHOP WRINKLES for Decorators, Painters, 
Paperh angers, and Others. By W. N. Brown. Crown 8vo. 
128 pp. Second Edition. Price 2s. 6d. net. (Post free, 2s. lOd. 
home ; 3s. abroad.) 

CASEIN. By Robert Scherer. Translated from the 
German by Chas. Salter. Demy 8vo. Illustrated. Second 
Revised English Edition. 160 pp. Price 7s. 6d. net. (Post free, 
8s. home ; 8s. 2d. abroad.) 

SIMPLE METHODS FOR TESTING PAINTERS* 
MATERIALS. By A. C. Wright, M.A. (Oxon.), 
B.Sc. (Lond.). Crown 8vo. 160 pp. Price 5s. net. (Post free, 
5s. 4d. home ; 5s. 7d. abroad.) 

IRON-CORROSION, ANTI-POULING AND ANTI- 
CORROSIVE PAINTS. Translated from the German 
of Louis Edgar And^s. Sixty-two Illustrations. 275 pp. 
Demy 8vo. Price 10s. 6dc net. (Post free, lis. home; 
lis. 4d. abroad.) 

THE TESTING AND VALUATION OP RAW 
MATERIALS USED IN PAINT AND COLOUR 
MANUFACTURE. By M. W. Jones, F.C.S. A 
Book for the Laboratories of Colour Works. 88 pp. Crown 8vo. 
Price 5s. net. (Post free, 5s. 4d. home and abroad.) 

For contents of these bookSy see List I, 



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THE MANUFACTURE AND COMPARATIVE 
MERITS OF WHITE LEAD AND 2INC WHITE 
PAINTS. By G. Petit, Civil Engineer, etc. Trans- 
lated from the French. Crown 8vo. 100 pp. Price 4s. net. 
(Post free, 4s. 4d. home ; 4s. 5d. abroad.) 

STUDENTS' HANDBOOK OF PAINTS, COLOURS, 
OILS AND VARNISHES. By John Furj^ell. 
Crown 8vo. 12 Illustrations. 96 pp. Price 2s. 6d. net. (Post 
free, 2s. lOd. home and abroad.) 

PREPARATION AND USES OF WHITE ZINC 
PAINTS. Translated from the French of P. Fleury. 
Crown 8vo. 280 pages. Price 6s. net. (Post free, 6s. 5d. home 
6s. 7d. abroad.) 



(Varnishes and Drying Oils.) 

THE MANUFACTURE OF VARNISHES AND 
KINDRED INDUSTRIES. By J. Geddes McIntosh. 
Second, greatly enlarged, English Edition, in three Volumes, 
based on and including the work of Ach. Livache. 

Volume I.— OIL CRUSHING, REFINING AND 
BOILING, THE MANUFACTURE OF LINO- 
LEUM, PRINTING AND LITHOGRAPHIC 
INKS, AND INDIA-RUBBER SUBSTITUTES. 

Demy 8vo. 150 pp. 29 Illustrations. Price 7s. 6d. net. 
(Post free. 8s. home ,' 8s. 2d. abroad.) 

Volume II.— VARNISH MATERIALS AND OIL- 
VARNISH MAKING. Demy 8vo. 70 Illustrations. 
220 pp. Price 10s. 6 J. net. (Post free, lis. home; lis. 4d. 
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Volume III.— SPIRIT VARNISHES AND SPIRIT 
VARNISH MATERIALS. Demy 8vo. Illustrated. 
464 pp. Price 12s. 6d. net. (Post free, 13s. Id. home ; 138. 7d. 
abroad.) 

DRYING OILS, BOILED OIL AND SOLID AND 
LIQUID DRIERS. By L. E. And^s. Expressly 
Written for this Series of Special Technical Books, and the 
Publishers hold the Copyright for English and Foreign Editions. 
Forty- two Illustrations. 342 pp. Demy 8vo. Price 12s. 6d. 
net. (Post free, 13s. Id. home ; 13s. 4d. abroad.) 

{Analysis of Resins, see page 9.) 



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(Oils, Fats, Waxes, Greases, Petroleum.) 

LUBRICATING OILS, FATS AND GREASES: 
Their Origin, Preparation, Properties, Uses and Analyses. A 
Handbook for Oil Manufacturers, Refiners and Merchants, and 
the Oil and Pat Industry in General. By George H. Hurst, 
F.C.S. Third Revised and Enlarged Edition. Seventy-four 
Illustrations. 384 pp. Demy 8vo. Price 10s. 6d. net. (Post 
free, lis. Id. home ; lis. 4d. abroad.) 

MINERAL WAXES: Their Preparation and Uses. By 
Rudolf Greoorius. Translated from the German. Crown 8vo. 
250 pp. 32 Illustrations. Price 6s. net. (Post free, 6s. 5d. 
home ; 68. 7d. abroad.) 

THE PRACTICAL COMPOUNDING OF OILS, 
TALLOW AND GREASE FOR LUBRICA. 
TION, ETC. By An Expert Oil Refiner. Second 
Edition. 100 pp. Demy 8vo. Price 7s. 6d. net. (Post free, 
8s. home ; 8s. 2d. abroad.) 

THE MANUFACTURE OF LUBRICANTS, SHOE 
POLISHES AND LEATHER DRESSINGS. By 

Richard Brunner. Translated from the Sixth German Edition 
by Chas. Salter. 10 Illustrations. Crown 8vo. 170 pp. Price 
78. 6d. net. (Post free, 8s. home ; 8s. 2d. abroad.) 

THE OIL MERCHANTS' MANUAL AND OIL 
TRADE READY RECKONER. Compiled by 
Prank F. Sherrifp. Second Edition Revised and Enlarged. 
Demy 8vo. 214 pp. With Two Sheets of Tables. Price 7s. 6d. 
net. (Post free, 8s. home ; 8s. 4d. abroad.) 

ANIMAL FATS AND OILS: Their Practical Pro- 
duction. Purification and Uses for a great Variety of Purposes. 
Their Properties, Falsification and Examination. Translated 
from the German of Louis Edgar And^s. Sixty-two Illustrations. 
240 pp. Second Edition, Revised and Enlarged. Demy 8vo. 
Price 10s. 6d. net. (Post free, Us. home ; lis. 4d. abroad.) 

VEGETABLE FATS AND OILS: Their Practical 
Preparation, Purification and Employment for Various Purposes, 
their Properties, Adulteration and Examination. Translated 
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trations. 340 pp. Second Edition. Demy 8vo. Price 10s. 6d. 
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EDIBLE FATS AND OILS : Their Composition, Manu- 
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C. A. Mitchell, B.A. (Oxon.). Demy 8vo. 150 pp. Price 
7s. 6d. net. (Post free, 8s. home ; 8s. 2d. abroad.) 

For contents of these hooks^ see List /. 



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7 

(Glycerine.) 

GLYCERINE: Its Production, Uses, and Examination. 
By S. W. KOPPE. Translated from the Second German Edition. 
260 pp. 7 Illustrations. Crown 8vo. Price 7s. 6d. net. (Post 
free, 8s. home ; 8s. 2d. abroad.) [y^st Published, 

(Essential Oils and Perfumes.) 

THE CHEMISTRY OF ESSENTIAL OILS AND 
ARTIFICIAL PERFUMES. By Ernest J. Parry, 
B.Sc. (Lond.), P.I.C, P.C.S. Second Edition, Revised and 
Enlarged. 552 pp. 20 Illustrations. Demy 8vo. Price 12s. 6d. 
net. (Post free, 13s. Id. home ; 13s. 7d. abroad.) ^ 

(Soap Manufacture.) 

SOAPS. A Practical Manual of the Manufacture of 
Domestic, Toilet and other Soaps. By George H. Hurst, P.C.S. 
2nd edition. 390 pp. 66 Illustrations. Demy 8vo. Price 12s. 6d. 
net. (Post free, 13s. Id. home ; 13s. 7d. abroad.) 

TEXTILE SOAPS AND OILS. Handbook on the 
Preparation, Properties and Analysis of the Soaps and Oils used 
in Textile Manufocturing, Dyeing and Printing. By George 
H. Hurst, P.C.S. Second Edition, Revised and partly re- 
written by W. H. Simmons, B.Sc. (Lond.). Demy 8vo. 200 pp. 
11 Illustrations. Price 7s. 6d. net. (Post free, 8s. home; 8s. 2d. 
abroad.) 

THE HANDBOOK OF SOAP MANUFACTURE. 

By Wm. H. Simmons, B.Sc. (Lond.), P.C.S., and H. A. Appleton. 
Demy 8vo. 160 pp. 27 Illustrations. Price 8s. 6d. net. (Post 
free, 9s. home ; 9s. 2d. abroad.) 

MANUAL OF TOILET SOAPMAKINO, including 
Medicated Soaps, Stain-removing Soaps, Metal Polishing Soaps, 
Soap Powders and Detergents. Translated from the German 
of Dr. C. Deite. Demy 4to. 150 pages. 79 Illustrations. 
Price 12s. 6d. net. (Post free, 13s. Id. home ; 13s. 7d. abroad.) 

(Cosmetical Preparations.) 

COSMETICS: MANUFACTURE, EMPLOYMENT 
AND TESTING OF ALL COSMETIC 
MATERIALS AND COSMETIC SPECIALITIES. 

Translated from the German of Dr. Theodor Roller. Crown 
8vo. 262 pp. Price 5s. net. (Post free, 5s. 5d. home; 5s. 7d. 
abroad.) 



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(Glue, Bone Products and Manures.) 

GLUE AND GLUE TESTING. By Samuel Rideal, 
D.Sc. (Lond.). Second Edition, Revised and Enlarged. Demy 
8vo. 196 pp. 14 Illustrations. Price 10s. 6d. net. (Post free, 
lis. home ; lis. 2d. abroad.) 

BONE PRODUCTS AND MANURES : An Account 
of the most recent Improvements in the Manufacture of Fat, 
Glue, Animal Charcoal, Size, Gelatine and Manures. By Thomas 
Lambert, Technical and Consulting Chemist. Second Revised 
Edition. Demy 8vo. 172 pages. 17 Illustrations. Price 7s. 6d. 
net. (Post free, 8s. home ; 8s. 2d. abroad.) 

{See also Chemical Manures^ p. 9.) 

• (Chemicals, Waste Products, etc,) 

REISSUE OF CHEMICAL ESSAYS OP C. W. 
SCHEELE. First Published in English in 1786. 
Translated from the Academy of Sciences at Stockholm, with 
Additions. 300 pp. Demy 8vo. Price 5s. net. (Post free, 5s. 7d. 
home ; 5s. lOd. abroad.) 

THE MANUFACTURE OP ALUM AND THE SUL- 
PHATES AND OTHER SALTS OF ALUMINA 
AND IRON. Their Uses and Applications as Mordants 
in Dyeing and Calico Printing, and their other Applications in 
the Arts, Manufactures, Sanitary Engineering, Agriculture and 
Horticulture. Translated from the French of Lucien Gesch- 
wiND. 195 Illustrations. 400 pp. Royal 8vo. Price 12s. 6d. 
net. (Post free, 13s. Id. home ; 13s. 7d. abroad.) 

AMMONIA AND ITS COMPOUNDS : Their Manu- 
facture and Uses. By Camille Vincent, Professor at the 
Central School of Arts and Manufactures, Paris. Translated 
from the French by M. J. Salter. Royal 8vo. 114 pp. Thirty- 
two Illustrations. Price 5s. net. (Post free, 5s. 5d. home; 
5s. 7d. abroad.) 

CHEMICAL WORKS: Their Design, Erection, and 
Equipment. By S. S. Dyson and S. S. Clarkson. Royal 8vo. 
220 pp. With 9 Folding Plates and bO Illustrations. Price 2l8. 
net. (Post free, 21s. 7d. home; 228. Id. abroad.) 

MANUAL OF CHEMICAL ANALYSIS, as applied to 
the Assay of Fuels, Ores, Metals, Alloys, Salts and other Mineral 
Products. By E. Prost, D.Sc; Translated by J. Cruickshank 
Smith, B.Sc. Royal 8vo. 300 pages. 44 Illustrations. Price 
12s. 6d. net. (Post free, 13s. Id. home ; 13s. 7d. abroad.) 

TESTING OF CHEMICAL REAGENTS FOR 
PURITY. Translated from the German of Dr. C. 
Krauch. Royal 8vo. 350 pages. Price 12s. 6d. net. .(Post free, 
13s. Id. home ; 13s. 7d. abroad.) 

For contents of these books, see List I, 



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9 

SHALE OILS AND TARS and their Products. By 
Dr. W. ScHEiTHAUBR. Translated from the German. Demy 8vo. 
190 pages. 70 Illustrations and 4 Diagrams. Price 8s. 6d. net. 
(Post free, 9s. home ; 9s. 2d. abroad.) 

THE BY-PRODUCTS OP COAL-GAS MANUFAC- 
TURE. ByK.R.LANGB. Translated from the German. 
Crown Svo. 164. pages. 13 Illustrations. Price5s.net. (Post 
free, 5s. 5d. home ; 5s. 7d. abroad.) 

INDUSTRIAL ALCOHOL. A Practical Manual on the 
Production and Use of Alcohol for Industrial Purposes and for 
Use as a Heating Agent, as an lUuminant and as a Source of 
Motive Power. By J. G. McIntosh. Demy Svo. 1907. 250 pp. 
With 75 Illustrations and 25 Tables. Price 7s. 6d. net. (Post 
free, 8s. home ; 8s. 4d. abroad.) 

THE UTILISATION OF WASTE PRODUCTS. A 

Treatise on the Rational Utilisation, Recovery and Treatment of 
Waste Products of all kinds. By Dr. Theodor Koller. Trans- 
lated from the Second Revised German Edition. Second English 
Revised Edition. Demy 8vo. 336 pp. 22 Illustrations. Price 
7s. 6d. net. (Post free, 8s. Id. home; Ss. 7d. abroad.) 

ANALYSIS OF RESINS AND BALSAMS. Trans- 
lated from the German of Dr. Karl Dibtbrich. Demy 8vo. 340 
pp. Price 7s. 6d. net. (Post free, 8s. home ; 8s. 4d. abroad.) 

DISTILLATION OF RESINS, RESINATE LAKES 
AND PIGMENTS, CARBON PIGMENTS AND 
PIGMENTS FOR TYPEWRITING MACHINES, 
'MANIFOLDERS, ETC. By Victor Schweizbr. 
Demy8vo. 185 pages. 68 Illustrations. Price7s.6d.net. (Post 
free, 8s. Id. home ; 8s. 4d. abroad.) 

DISINFECTION AND DISINFECTANTS. By M. 

Christian. Translated from the German. Crown Svo. 112 
pages. 18 Illustrations. Price 5s. net. (Post &ee, 5s. 4d. home ; 
5s. 7d. abroad.) 

(Agricultural Chemistry and Manures.) 

MANUAL OF AGRICULTURAL CHEMISTRY. By 

Herbert Inole, P.I.C, Late Lecturer on Agricultural Chemistry, 
the Leeds University; Lecturer in the Victoria University. 
Third and Revised Edition. 400 pp. 16 Illustrations. Demy 
8vo. Price 7s. 6d. net. (Post free, 8s. Id. home ; 8s. 7d. abroad.) 

CHEMICAL MANURES. Translated from the French 
of J. Fritsch. Demy Svo. Illustrated. 340 pp. Price 10s. 6d, 
net. (Post free, lis. Id. home; lis. 7d. abroad.) 

(See also Bone Products and Manures, p, 8.| 



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10 

(Writing Inks and Sealing Waxes.) 

INK MANUFACTURE: Including Writing, Copying, 
Lithographic, Marking, Stamping and Laundry Inks. By 
SiOMUND Lbhnbr. Translated from the German of the Fifth 
Edition. Second Revised and Enlarged English Edition. 
Crown 8vo. 180 pages. Three Illustrations. Price 5s. net. (Post 
free, 5s. 4d. home ; 5s. 7d. abroad.) 

SEALING-WAXES, WAFERS AND OTHER 
ADHESIVES FOR THE HOUSEHOLD, OFFICE, 
WORKSHOP AND FACTORY. By H. C. Standage. 
Crown 8vo. 96 pp. Price 5s. net. (Post free, 5s. 4d. home; 
5s. 5d. abroad.) 

(Lead Ores and Lead Compounds.) 

LEAD AND ITS COMPOUNDS. By Thos. Lambert, 
Technical and Consulting Chemist. Demy 8vo. 226 pp. Forty 
Illustrations. Price 7s. 6d. net. (Post free, 8s. home ; 8s. 4d. 
abroad.) 

NOTES ON LEAD ORES : Their Distribution and Pro- 
perties. By Jas. Pairib, F.G.S. Crown 8vo. 64 pages. Price 
Is. net. (Post free, Is. 4d. home ; Is. 5d. abroad.) 

{White Lead and Zinc White Paints, see p, 5.) 

(Industrial Hygiene.) 

THE RISKS AND DANGERS TO HEALTH OF 
VARIOUS OCCUPATIONS AND THEIR PRE- 
VENTION. By Leonard A. Parry, M.D., B.Sc. 
(Lond.). 196 pp. Demy Svo. Price 7s. 6d. net. (Post free. 



ny J 

>d.) 



88. home ; 8s. 2d. abroa( 

(Industrial Uses of Air, Steam and 
Water.) 

DRYING BY MEANS OF AIR AND STEAM. Ex- 
planations, Formulae, and Tables for Use in Practice. Trans- 
lated from the German of E. Hausbrand. Second Revised 
English Edition. Two folding Diagrams, Thirteen Tables, and 
Two Illustrations. Crown Svo. 76 pp. Price 5s. net. (Post 
free, 5s. 4d. home ; 5s. 7d. abroad.) 
(See also " Evaporating^ Condensing and Cooling Apparatus^''* p. 18.) 

PURE AIR, OZONE AND WATER. A Practical 
Treatise of their Utilisation and Value in Oil, Grease, Soap, Paint, 
Glue and other Industries. By W. B. Cowell. Twelve Illus- 
trations. Crown Svo. 85 pp. Price 5s. net. (Post free, 5s. 4d. 
home ; 5s. 7d. abroad. ) 

For contents of these hooks, see List III, 



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11 

THE INDUSTRIAL USES OF WATER. COMPOSI- 
TION— EFFECTS— TROUBLES— REMEDIES— 
RESIDUARY WATERS— PURIFICATION— AN- 
ALYSIS. By H. DE LA Coux. Royal 8vo. Trans- 
lated from tjie French and Revised by Arthur Morris. 364 pp. 
135 Illustrations. Price 10s. 6d. net. (Post free, lis. Id. home; 
lis. 7d. abroad.) 
(See Books on Smoke Prevention, Engineering and Metallurgy, p. 18.) 

(X Rays.) 

PRACTICAL X RAY WORK. By Frank T. Addyman, 
B.Sc. (Lond.), P.I.C, Member of the Roentgen Society of London ; 
Radiographer to St. George's Hospital ; Demonstrator of Physics 
and Chemistry, and Teacher of Radiography in St. George's 
Hospital Medical School. Demy 8vo. Twelve Plates from 
Photographs of X Ray Work. Fitty-two Illustrations. 200 pp. 
Price lOs. 6d. net. (Post free, lis. home; lis. 4d. abroad.) 

(India- Rubber and Gutta Percha.) 

INDIA-RUBBER AND OUTTA PERCHA. Second 
English Edition, Revised and Enlarged. Based on the French 
work of T. Sbeliomann, G. Lamy Torrilhon and H. Falcqnnet 
by John Geddbs McIntosh. Royal 8vo. 100 Illustrations. 400 
pages. Price 12s. 6d. net. (Post free, 13s. Id. home ; 13s. 7d. 
abroad.) 

(Leather Trades.) 

THE LEATHER WORKER'S MANUAL. Being a 
Compendium of Practical Recipes and Working Formulae for 
Curriers, Bootmakers, Leather Dressers, Blacking Manufac- 
turers, Saddlers, Fancy Leather Workers. By H. C. Standaoe. 
Demy 8vo. 165 pp. Price 7s. 6d. net. (Post free, 8s. home; 
8s. 2d. abroad.) 
(See also Manufacture of Shoe Polishes, Leather Dressings, etc., /. 6.) 

(Pottery, Bricks, Tiles, Glass, etc.) 

MODERN BRICKMAKINO. By Alfred B. Sbarle, 
Royal 8vo. 440 pages. 260 Illustrations. Price 12s. 6d. net. 
(Post free, 13s. Id. home; 13s. 7d. abroad.) 

THE MANUAL OP PRACTICAL POTTING. Com- 
piled by Experts, and Edited by Chas. F. Binns. Fourth Edition, 
Revised and Enlarged. 200 pp. Demy 8vo. Price 17s. 6d. net. 
(Post free, 18s. home ; 18s. 4d. abroad.) 

POTTERY DECORATING. A Description of all the Pro- 
cesses for Decorating Pottery and Porcelain. By R. Hainbach. 
Translated from the German. Crown 8vo. 250 pp. Twenty- 
two Illustrations. Price 7s. 6d. net. (Post free, 8s. home ; 
8s. 2d. abroad.) 



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12 

A TREATISE ON CERAMIC INDUSTRIES. A 

Complete Manual for Pottery, Tile, and Brick Manufacturers. By 
Emilb Bourry. a Revised Translation fi*om the French, with 
some Critical Notes by Alfred B. Sbarlb. Demy 8vo. 308 
Illustrations. 460 pp. Price 12s. 6d. net. (Post free, ISs. Id. 
home ; 13s. 7d. abroad.) 

ARCHITECTURAL POTTERY. Bricks, Tiles, Pipes, 
Enamelled Terra-cottas, Ordinary and Incrusted Quarries, Stone- 
ware Mosaics, Faiences and Architectural Stoneware. By I. eon 
LEpfivRB. Translated from the French by K. H. Bird, M.A., 
and W. MooRB Binns. With Five Plates. 950 Illustrations in 
the Text, and numerous estimates. 500 pp. Royal 8vo. Price 
15s. net. (Post free, 15s. 7d. home ; 16s. 7d. abroad.) 

THE ART OF RIVETING GLASS, CHINA AND 
EARTHENWARE. By J. Howorth. Second 
Edition. Paper Cover. Pncels.net. (By post, home or abroad. 
Is. 3d.) 

NOTES ON POTTERY CLAYS. The Distribution, 
Properties, Uses and Analyses of Ball Clays,* China Clays and 
China Stone. By J as. Fairib, F.G.S. 132 pp. Crown 8vo. 
Price 3s. 6d. net. (Post free, 3s. lOd. home ; 4s. abroad.) 

HOW TO ANALYSE CLAY. By H. M. Ashby. Demy 
8vo. 72 pp. 20 Illustrations. Price 3s. 6d. net. (Post free, 
38. lOd. home ; 4s. abroad.) 

A Beissue of 

THE HISTORY OF THE STAFFORDSHIRE POT- 
TERIES; AND THE RISE AND PROGRESS 
OF THE MANUFACTURE OF POTTERY AND 
PORCELAIN. With References to Genuine Specimens, 
and Notices of Eminent Potters. By Simeon Shaw. (Originally 
published in 1829.) 265 pp. Demy 8vo. Price 5s. net. (Post 
free, Ss. 5d. home ; 5s. lOd. abroad.) 

A Reissue of 

THE CHEMISTRY OF THE SEVERAL NATURAL 
AND ARTIFICIAL HETEROGENEOUS COM- 
POUNDS USED IN MANUFACTURING POR- 
CELAIN, GLASS AND POTTERY. By Simeon 
Shaw. (Originally published in 1837.) 750 pp. Royal 8vo. 
Price 10s. net. (Post free, 10s. 7d. home ; 12s. Id. abroad.) 

BRITISH POTTERY MARKS. By G. Woolliscroft 
Rhbao. Demy 8vo. 310 pp. With over Twelve-hundred Illus- 
trations of Marks. Price 7s. 6d. net. (Post free, 8s. Id. home ; 
8s. 4d. abroad.) 

For contents of these books, see List J J J. 



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13 

(Glassware, Glass Staining and Painting.) 

RECIPES FOR FLINT GLASS MAKING. By a 

British Glass Master and Mixer. Sixty Recipes. Being Leaves 
from the Mixing Book of several experts in the Flint Glass Trade, 
containing up-to-date recipes and valuable information as to 
Crystal, Demi-crystal and Coloured Glass in its many varieties. 
It contains the recipes for cheap metal suited to pressing, blow- 
ing, etc., as well as the most costly crystal and ruby. Second 
, Edition. Crown 8vo. Price 10s. 6d. net. (Post free, 10s. lOd. 
home; lis. abroad.) 

A TREATISE ON THE ART OF GLASS PAINT- 
ING. Prefaced with a Review of Ancient Glass. By 
Ernest R. Supflino. With One Coloured Plate and Thirty- 
seven Illustrations. Demy 8vo. 140 pp. Price 7s. 6d. net. 
(Post free, 8s. home ; 8s. 2d. abroad.) 

(Paper Making and Testing.) 

THE PAPER MILL CHEMIST. By Henry P. Stevens, 
M.A., Ph.D., P.I.C. Royal 12mo. 60 Illustrations. 300 pp. 
Price 7s. 6d. net. (Post free, 7s. lOd. home ; 8s. abroad.) 

THE TREATMENT QF PAPER FOR SPECIAL 
PURPOSES. By L. E. And6s. Translated from the 
German. Crown 8vo. 48 Illustrations. 250 pp. Price 6s. net. 
(Post free, 6s. 5d. home ; 6s. 7d. abroad.) 

(Enamelling on Metal.) 

ENAMELS AND ENAMELLING. For Enamel 
Makers, Workers in Gold and Silver, and Manufacturers of 
Objects of Art. By Paul Randau. Second and Revised 
Edition. Translated &om the German. With 16 Illustrations. 
Demy 8vo. 200 pp. Price 10s. 6d. net. (Post free, lis. home; 
Us. 2d. abroad.) 

THE ART OF ENAMELLING ON METAL. By 
W. Norman Brown. Second Edition, Revised. Crown 8vo. 
60 pp. Price 3s. 6d. net. (Post free, 3s. lOd. home ; 4s. abroad.) 

(Textile Subjects.) 

THE FINISHING OP TEXTILE FABRICS (Woollen, 
Worsted, Union, and other Cloths). By Roberts Beaumont, 
M.Sc, M.I.Mech.E. With 150 Illustrations of Fibres, Yarns 
and Fabrics, also Sectional and other Drawings of Finishing 
Machinery. Demy 8vo. 260 pp. Price 10s. 6d. net. (Post free, 
Us. home; lis. 4d. abroad.) 

STANDARD CLOTHS: Structure and Manufacture 
(General, Military and Naval). By Roberts Beaumont, M.Sc, 
M.I.Mech.E. 342 pp. Numerous Illustrations. 16 Plates in 
Monochrome and Colour. Demy 8vo. Price 12s. 6d. net. (Post 
free, 13s. Id. home ; 14s. Id. abroad.) [7^ ^^ published. 



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14 

FIBRES USED IN TEXTILE AND ALLIED IN- 
DUSTRIES. By C. Ainsworth Mitchell, B.A. 
(Oxon.), F.I.C., and R. M. Prideaux, F.I.C. With 66 Illustra- 
tions specially drawn direct from the Fibres. Demy 8vo. 
200 pp. Price 7s. 6d. net. (Post free, 8s. home ; 8s. 2d. abroad.) 

DRESSINGS AND FINISHINGS FOR TEXTILE 
FABRICS AND THEIR APPLICATION. De- 

scription of all the Materials used in Dressing Textiles : Their 
Special Properties, the preparation of Dressings and their em- 
ployment in Finishing Linen, Cotton, WooUep and Silk Fabrics. 
Fireproof and Waterproof Dressings, together with the principal 
machinery employed. Translated from the Third German 
Edition of Fribdrich Polleyn. Demy 8vo. 280 pp. Sixty 
Illustrations. Price 7s. 6d. net. (Post free, 8s. home; 8s. 2d. 
abroad.) 

THE CHEMICAL TECHNOLOGY OF TEXTILE 
FIBRES : Their Origin, Structure, Preparation, Wash- 
ing, Bleaching, Dyeing, Printing and Dressing. By Dr. Georo 
VON Gboroibvics. Translated from the German by Charles 
Salter. 320 pp. Forty-seven Illustrations. Royal 8vo. Price 
10s. 6d. net. (Post free, lis. Id. home ; lis. 4d. abroad.) 

POWER.LOOM WEAVING AND YARN NUMBER- 
ING, According to Various Systems, with Conversion 
Tables. Translated from the German of Anthon Gruner. With 
Twenty-8lx Diagrams In Colours. 150 pp. Crown 8vo. Price 
7s. 6d. net. (Post free, 7s. lOd. home ; 8s. Id. abroad.) 

TEXTILE RAW MATERIALS AND THEIR CON- 
VERSION INTO YARNS. (The Study of the Raw 
Materials and the Technology of the Spinning Process.) By 
Julius Zipser. Translated from German by Charles Salter. 
302 Illustrations. 500 pp. Demy 8vo. Price 10s. 6d. net. 
(Post free, lis. Id. home ; lis. 7d. abroad.) 

GRAMMAR OF TEXTILE DESIGN. By H. Nisbbt, 
Weaving and Designing Master, Bolton Municipal Technical 
School. Demy 8vo. 280 pp. 490 Illustrations and Diagrams. 
Price 6s. net. (Post free, 6s. 5d. home ; 6s. 7d. abroad.) 

ART NEEDLEWORK AND DESIGN. POINT 
LACE. A Manual of Applied Art for Secondary Schools 
and Continuation Classes. By M. E. Wilkinson. Oblong 
quarto. With 22 Plates. Bound in Art Linen. Price 3s. 6d. 
net. (Post free, 4s. home ; 4s. 2d. abroad.) 

HOME LACE-MAKING. A Handbook for Teachers and 
Pupils. By M. E. W. Milroy. Crown 8vo. 64 pp. With 3 
Plates and 9 Diagrams. Price Is. net. (Post free, Is. 4d. home ; 
Is. 5d. abroad.) 

CHURCH LACE. By M. E. W. Milroy. [In preparation. 
For contents of these books^ see List II, 



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15 

THE CHEMISTRY OF HAT MANUFACTURING. 

Lectures delivered before the Hat Manufacturers' Association. 

By Watson Smith, F.C.S., F.I.C. Revised and Edited by 

Albert Shonk. Crown 8vo. 132 pp. 16 Illustrations. Price 

78. 6d. net. (Post free, 7s. lOd. home ; 8s. abroad.) 
THE TECHNICAL TESTING OF YARNS AND 

TEXTILE FABRICS. With Reference to Official 

Specifications. Translated from the German of Dr. J. Herzfbld. 

Second Edition. Sixty-nine Illustrations. 200 pp. Demy 8vo. 

Price 10s. 6d. net. (Post free, lis. home; lis. 2d. abroad.) 
DECORATIVE AND FANCY TEXTILE FABRICS. 

By R. T. Lord. For Manufacturers and Designers of Carpets, 

Damask, Dress and all Textile Fabrics. 200 pp. Demy 8vo. 

132 Designs and Illustrations. Price 7s. 6d. net. (Post free, 

8s. home; Ss. 2d. abroad.) 
THEORY AND PRACTICE OF DAMASK WEAV- 

ING. By H. KiNZER and K. Walter. Royal 8vo. 

Eighteen Folding Plates. Six Illustrations. Translated from 

the Geraian. 1 10 pp. Price 8s. 6d. net. (Post free, 9s. Id. home ; 

9s. 7d. abroad.) 

FAULTS IN THE MANUFACTURE OF WOOLLEN 
GOODS AND THEIR PREVENTION. By 

Nicolas Reiser. Translated from the Second German Edition. 
Crown 8vo. Sixty-three Illustrations. 170 pp. Price 5s. net. 
(Post free, 5s. 5d. home ; 5s. 7d. abroad.) 

SPINNING AND WEAVING CALCULATIONS, 

especially relating to Woollens. From the German of N. 
Reiser. Thirty-four Illustrations. Tables. 160 pp. Demy 
8vo. 1904. Price 10s.6d.net. (Post free, lis. home; lis. Id. 
abroad.) 

WORSTED SPINNERS' PRACTICAL HANDBOOK. 

By H. Turner. 148 pp. 54 Drawings. Crown 8vo. Price 68. 
net. (Post free, 6s. 5d. home ; 6s. 8d. abroad.) [^ust published, 

ANALYSIS OF WOVEN FABRICS. By A. P. Barker, 
M.Sc., and E. Midgley. Demy 8vo. 316 pp. Numerous Tables, 
Examples and 82 Illustrations. Price 7s. 6d. net. (Post free, 
8s. home ; 8s. 2d. abroad.) 

WATERPROOFING OF FABRICS. By Dr. S. Mier- 
ziNSKi. Second Edition, Revised and Enlarged. Crown 8vo. 
140 pp. 29 Illus. Price 5s. net. (Post free, 58. 5d. home; 
5s. 7d. abroad.) 

HOW TO MAKE A WOOLLEN MILL PAY. By 
John Mackie. Crown 8vo. 76 pp. Price 3s. 6d. net. (Post 
free, 3s. lOd. home; 4s. abroad.) 

YARN AND WARP SIZING IN ALL ITS 
BRANCHES. Translated from the German of Carl 
Kretschmar. Royal 8vo. 123 Illustrations. 150 pp. Price 
10s. 6d. net. (Post free, lis. home; lis. 2d. abroad.) 
{For " Textile Soaps and Oils " see p. 7.) 



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16 

(Dyeing, Colour Printing, Matching 
and Dye-stuffs.) 

THE COLOUR PRINTING OF CARPET YARNS. 

Manual for Colour Chemists and Textile Printers. By David 
Patbrson, P.C.S. Seventeen Illustrations. 136 pp. Demy 
8vo. Price 7s. 6d. net. (Post free, 8s. home ; 8s. 2d. abroad.) 

TEXTILE COLOUR MIXING. By David Paterson, 
F.R.S.E., F.C.S. Formerly published under title of '* Science of 
Colour Mixing ". Second Revised Edition. Demy 8vo. 140 pp. 
41 Illustrations, with 5 Coloured Plates and 4 Plates showing 
Dyed Specimens. Price 7s. 6d. net. (Post free, 8s. home ; 
8s. 2d. abroad.) [jfust published. 

DYERS' MATERIALS : An Introduction to the Examina- 
tion, Evaluation and Application of the most important Sub- 
stances used in Dyeing, Printing, Bleaching and Finishing. By 
Paul Hberman, Ph.D. Translated from the German by A. C. 
Wright, M.A. (Oxon)., B.Sc. (Lond.). Twenty-four Illustrations. 
Crown 8vo. 150 pp. Price 5s. net. (Post free, 5s. 5d. home ; 
5s. 7d. abroad.) 

COLOUR MATCHING ON TEXTILES. A Manual 
intended for the use of Students of Colour Chemistry, Dyeing and 
Textile Printing. By David Paterson, F.C.S. Coloured Frontis- 
piece. Twenty-nine Illustrations and Fourteen Speolmene Of 
Dyed Fabrioe. Demv 8vo. 132 pp. Price 7s. 6d. net. (Post 
free, 8s. home ; 8s. 2cl. abroad.) 

COLOUR : A HANDBOOK OF THE THEORY OF 
COLOUR. By George H. Hurst, F.C.S. With Ten 
Coloured Platee and Seventy-two Illustrations. 160 pp. Demy 
8vo. Price 7s. 6d. net. (Post free, 8s. home ; 8s. 2d. abroad.) 

77 f\\ Attn A f\^ 

THE ART OF DYEING WOOL, SILK AND 
COTTON. Translated from the French of M. Hellot, 
M. Macqubr and M. lb Pileur D*Aplic{ny. First Published in 
English in 1789. Six Plates. Demy 8vo. 446 pp. Price 5s. net. 
(Post free, Ss. 7d. home; 6s. Id. abroad.) 

THE CHEMISTRY OP DYE-STUFFS. By Dr. Georo 
Von Gboroibvics. Translated from the Second German Edition. 
412 pp. Demy 8vo. Price 10s. 6d. net. (Post free, lis. Id. 
home; lis. 7d. abroad.) 

THE DYEING OF COTTON FABRICS : A Practical 

Handbook for the Dyer and Student. By Frankun Bbbch, 

Practical Colourist and Chemist. 272 pp. Forty-four Illus- 

. trations of Bleaching and Dyeing Machinery. Demy 8vo. Price 

7s. 6d. net. (Post free, 8s. home ; 8s. 2d. abroad.) 

THE DYEING OF WOOLLEN FABRICS. By 
Franklin Bbbch, Practical Colourist and Chemist. Thirty- 
three Illustrations. Demy 8vo. 228 pp. Price 7s. 6d. net. 
(Post free, 8s. home ; 8s. 2d. abroad.) 

For contents of these books, see List II. 



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(Silk Manufacture.) 

SILK THROWING AND WASTE SILK SPIN- 
NING. By HoLLiNS Rayner. Demy 8vo. 170 pp. 
117 lUus. Price 5s. net. (Post free, 5s. 5d. home ; 5s. 7d. abroad.) 

(Bleaching and Bleaching Agents.) 

A PRACTICAL TREATISE ON THE BLEACHING 
OP LINEN AND COTTON YARN AND FABRICS. 

By L. Tailfer, Chemical and Mechanical Engineer. Trans- 
lated from the French by John Geddes McIntosh. Demy 8vo. 
303 pp. Twenty Illus. Price 123. 6d.. net. (Post free, 13s. Id. 
home; 13s. 7d. abroad.) 
MODERN BLEACHING AGENTS AND DETER- 
GENTS. By Professor Max Bottler. Translated 
from the German. Crown 8vo. 16 Illustrations. 160 pages. 
Price 5s. net. (Post free, 5s. 4d. home ; 5s. 7d. abroad.) 

(Cotton Spinning, Cotton Waste and 
Cotton Combing.) 

COTTON SPINNING (First 'Year). By Thomas 

Thornley, Spinning Master, Bolton Technical School. 160 pp. 

84 Illustrations. Crown 8vo. Second Impression. Price 3s. 

net. (Post free, 3s. 5d. home; 3s. 7d. abroad.) 
COTTON SPINNING (Intermediate, or Second Year). 

By T. Thornley. Third Edition, Revised and Enlarged. 320 pp. 

114 Drawings. Crown 8vo. Price 7s. 6d. net. (Post free, 8s. 

home ; 8s. 2d. abroad.) [^ust Published. 

COTTON SPINNING (Honours, or Third Year). By 

T. Thornley. 216 pp. 74 Illustrations. Crown 8vo. Second 

Edition. Price 5s. net. (Post free, 5s. 5d. home; 5s. 7d. abroad.) 
COTTON COMBING MACHINES. By Thos. Thorn- 

LEY, Spinning Master, Technical School, Bolton. Demy 8vo. 

117 Illustrations. 300 pp. Price7s.6d.net. (Post free, 8s. Id. 

home ; 8s. 7d. abroad.) 
COTTON WASTE : Its Production, Characteristics, 

Regulation, Opening, Carding, Spinning and Weaving. By Thomas 

Thornley. Demy 8vo. 286 pages. 60 Illustrations. Price 7s. 6d. 

net. (Post free, 8s. home ; 8s. 2d. abroad.) 
THE RING SPINNING FRAME : GUIDE FOR 
OVERLOOKERS AND STUDENTS. By N. Booth. 

Crown 8vo. 76 pages. Price 3s. net. (Post free, 3s. 4d. home ; 

3s. 7d. abroad.) 

(Flax, Hemp and Jute Spinning.) 

MODERN FLAX, HEMP AND JUTE SPINNING 
AND TWISTING. A Practical Handbook for the use 
of Flax, Hemp and Jute Spinners, Thread, Twine and Rope 
Makers. By Herbert R. Carter, Mill Manager, Textile Expert 
and Engineer, Examiner in Flax Spinning to the City and Guilds of 
London Institute. Demy 8vo. 1907. With 92 Illustrations. 200 
pp. Price 7s. 6d. net. (Post free, 7s. lOd. home; 8s. Id. abroad.) 



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(Collieries and Mines.) 

RECOVERY WORK AFTER PIT FIRES. By Robert 
Lamprbcht, Mining Engineer and Manager. Translated from 
the German. Illustrated by Six large Plates, containing Seventy- 
six Illustrations. 175 pp. Demy 8vo. Price 10s. 6d. net. (Post 
free. lis. home; lis. 2d. abroad.) 

VENTILATION IN MINES. By Robert Wabnbr, 
Mining Engineer. Translated from the German. Royal 8vo. 
Thirty Plates and Twenty-two Illustrations. 240 pp. Price 
lOs. 6d. net. (Post free, lis. Id. home; lis. 4d. abroad.) 

THE ELECTRICAL EQUIPMENT OF COLLIERIES. 
By W. Galloway Duncan and David Penman. Demy 8vo. 
310 pp. 155 Illustrations and Diagrams. Price 10s. 6d. net. 
(Post free, lis. Id. home; lis. 4d. abroad.) 

(Dental Metallurgy.) 

DENTAL METALLURGY: MANUAL FOR STU- 
DENTS AND DENTISTS. By A. B. Griffiths, 
Ph.D. Demy 8vo. Thirty-six Illustrations. 200 pp. Price 
7s. 6d. net. (Post free, 8s. home ; 8s. 2d. abroad.) 

(Engineering, Smoke Prevention ^nd 
Metallurgy.) 

THE PREVENTION OF SMOKE. Combined with 
the Economical Combustion of Fuel. By W. C. Popplewbll*. 
M.Sc, A.M. Inst., C.E., Consulting Engineer. Portv-six Illus- 
trations. 190 pp. Demy 8vo. Price 7s. 6d. net. (Post free, 
8s. home ; 8s. 4d. abroad.) 

GAS AND COAL DUST FIRING. A Critical Review 
of the Various Appliances Patented in Germany for this purpose 
since 1885. By Albert POtsch. 130 pp. Demy 8vo. Trans- 
lated from the German. With 103 Illustrations. Price 5s. net. 
(Post free, 5s. 5d. home ; 5s. 7d. abroad.) 

THE HARDENING AND TEMPERING OF STEEL 
IN THEORY AND PRACTICE. By Pridoun 
Reiser. Translated from the German of the Third Editioa. 
Crown 8vo. 120 pp. Price 5s. net. (Post free, 5s. 4d. home; 
5s. 5d. abroad.) 

SIDEROLOGY: THE SCIENCE OF IRON (The 
Constitution of Iron Alloys and Slags). Translated from 
German of Hanns Freiherr v. JUptnbr. 350 pp. Demy Svo. 
Eleven Plates and Ten Illustrations. Price 10s. 6d. net. (Post 
free, lis. Id. home; lis. 7d. abroad.) 

EVAPORATING, CONDENSING AND COOLING 
APPARATUS. Explanations, Formulae and Tables 
for Use in Practice. By E. Hausbrand, Engineer. Translated 
by A. C. Wright, M.A. (Oxon.), B.Sc. (Lond.). With Twenty- 
one Illustrations and Seventy-six Tables. 400 pp. Demy 8vo» 
Price 10s. 6d. net. (Post free, lis. Id. home; lis. 7d. abroad.) 

For contents of these books, see Lists II and III, 



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(The "Broadway." Series of Engineering 
Handbooks.) 

Uniform in Size : Narrow Crown 8vo. (Pocket 5ize.) 
Volume I.— ELEMENTARY PRINCIPLES OF RE- 
INFORCED CONCRETE CONSTRUCTION. By 

EwartS. Andrews, B.Sc. Eng. (Lond.). 200 pages. With 57 
Illustrations. Numerous Tables and Worked Examples. Price 
3s. net. (Post free, ds. 4d. home ; Ss. 7d. abroad.) 

Volume II.— GAS AND OIL ENGINES. By A. 
KiRSCHKB. Translated and Revised from the German, and 
adapted to British practice. 160 pages. 55 Illustrations. 
Price 3s. net. (Post free,. 3s. 4d. home ; Ss. 7d. abroad.) 

Volume III. — IRON AND STEEL CONSTRUC- 
TIONAL WORK. By K. Schindler. Translated 
and Revised from the German, and adapted to British practice. 
140 pages. 115 Illustrations. Price Ss. 6d. net. (Post free, 
3s. lOd. home ; 4s. Id. abroad.) 

Volume IV.— TOOTHED GEARING. By G. T. White, 
B.Sc. (Lond.). 220 pages. 136 Illustrations. Price 38. 6d. net. 
(Post free, 3s. lOd. home ; 4s. Id. abroad.) 

Volume V.— STEAM TURBINES : Their Theory and 
Construction. By . H. Wilda. Translated from the German ; 
Revised and adapted to British practice. 200 pages. 104 Illustra- 
tions. Price 3s. 6d. net. (Post free, 3s. lOd. home ; 4s. Id. abroad.) 

Volume VI.— CRANES AND HOISTS. Their Construc- 
tion and Calculation. By H. Wilda. Translated from the German ; 
revised and adapted to British practice. 168 pages. 399 lUustra- 
tionst Price 3s. 6d. net. (Post free, 3s. lOd. home ; 4s. Id. abroad.) 

Volume VII.— FOUNDRY MACHINERY. By E. 
Trbibbr. Translated from the German ; revised and adapted to 
British practice. 148 pages. 51 Illustrations. Price 3s. 6d. net. 
(Post free, 3s. lOd. home ; 4s. Id. abroad.) 

Volume VIII.— MOTOR CAR MECHANISM. By 
W. E. DOMMETT, Wh.Ex., A.M.I.A.E. 200 pages. 102 Illustra- 
tions. Price 3s. 6d..net. (Post free, 3s. lOd. home ; 4s. Id. abroad.) 

Volume IX.— ELEMENTARY PRINCIPLES OF 
ILLUMINATION AND ARTIFICIAL LIGHTING. 
By A. Blok, B.Sc. 240 pages. 124 Illustrations and Diagrams 
and 1 Folding Plate. Price 3s. 6d. net. (Post free, 3s. lOd. 
home ; 4s. Id. abroad.) 

Volume X.— HYDRAULIC S. By E. H. Sprague, 
A.M.I.C.E. 190 pages. With Worked Examples and 89 Illustra- 
tions. Price 3s. 6d. net. (Post free, 3s. lOd. home ; 4s. Id. abroad.) 

Volume XI. — ELEMENTARY PRINCIPLES OF 
SURVEYING. By M. T. M. Ormsby, M.I.C.E.I. 
244 pages. With Worked Examples and 135 Illustrations and 
Diagrams, including 4 Folding Plates. Price 4s. net. (Post free, 
4s. 4d. home; 4s. 7d. abroad.) 

Volume XII.— THE SCIENCE OF WORKS MANAGE- 

• MFiNT. By John Batey. 232 pages. Price 48. net. 
(Post free, 4s. 4d. home ; 4s. 7d. abroad.) 



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Volume XIII.— THE CALCULUS FOR ENGINEERS. 

By EwART S. ' Andrews, B.ScEng. (Lond.), and H. Bryon 
Heywood, D.Sc. (Paris), B.Sc. (Lond.). 284 pages. 102 Illustra- 
tions. With Tables and Worked Examples. Price 4s. net. (Post 
free, 4s. 4d. home ; 4s. 7d. abroad.) 

Volume XIV. — LATHES : Their Construction and 
Operation. By G. W. Burlev, Wh.Ex., A.M.I.M.E. 244 pages. 
200 Illustrations. Price 3s. 6d. net. (Post free, 3s. lOd. home ; 
4s. Id. abroad.) 

Volume XV.— STEAM BOILERS AND COMBUS- 
TION. By John Batey. 220 pages. 18 Diagrams. 
Price 4s. net. (Post free, 4s. 4d. home ; 4s. 7d. abroad.) 

Volume XVI.— REINFORCED CONCRETE IN PRAC- 
TICE. By A. Alban H. Scott, M.S.A., M.C.I. 190 pp. 
130 Illustrations and Diagrams and 2 Folding Plates. Price 4s. 
net. (Post free, .4s. 4d. home ; 4s. 7d. abroad.) 

Volume XVII. — STABILITY OP MASONRY. By 
E. H. Sprague, A.M.I.C.E. 180 pp. 92 Illustrations. 3 Folding 
Plates and Worked Examples. Price 4s. net. (Post free, 4s. 4d. 
home; 4s. 7d. abroad.) [^ust published. 

Volume XVIII.— TESTING OP MACHINE TOOLS. 

By G. W. BURLEY, Wh.Ex., A.M.I.M.E. 240 pp. 110 Illustra- 
tions. Price 4s. net. (Post free, 4s. 4d. home ; 4s. 7d. abroad.) 



[yust published. 



Volume XIX.— BRIDGE POUNDATIONS. By W. 

BuRNSiDE, M.I.C.E. 148 pp. 31 Diagrams. Price4s.net. (Post 
free, 4s. 4d. home ; 4s. 7d. abroad.) [^ust published. 

[IN PREPARATION.] 
PORTLAND CEMENT. Its Properties and Manu- 
facture. By P. C. H. West, F.C.S. 
CALCULATIONS POR A STEEL PRAME BXnLD- 

ING. By W. C. Cocking, M.C.I. 
GEAR GUTTING. By G. W. Burley, Wh.Ex., 

A.M.I.M.E. 
MOVING LOADS BY INPLUENCE LINES AND 

OTHER METHODS. By E. H. S?rague, A.M.LC.E. 
THE STABILITY OP ARCHES. By E. H. Sprague, 

A.M.I.C.E. 
DRAWING OPPICE PRACTICE. By W. Clegg. 
ESTIMATING STEELWORK POR BUILDINGS. By 

B. P. F. Gleed and S. Bylander, M.C.I. 
THE THEORY OP THE CENTRIPUGAL AND 

TURBO PUMP. By J. Wells. 
STRENGTH OP SHIPS. By James Bertram Thomas. 
MACHINE SHOP PRACTICE. By G. W. Burley, 

Wh.Ex., A.M.I.M.E. 

DESIGN OP MACHINE ELEMENTS (In 2 Volumes). 

By W. G. DUNKLEY. 

IRON AND STEEL. By J. S. Glen Primrose. 

For contents of these books ^ see List III, 



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21 

(Sanitary Plumbing, Metal Work, etc.) 

EXTERNAL PLUMBING WORK. A Treatise on 
Lead Work for Roofs. By John W. Hart, R.P.C. 180 Illustra- 
tions. 272 pp. Demy 8vo. Second Edition Revised. Price 
7s. 6d. net. (Post free, 8s. home ; 8s. 2d. abroad.) 

HINTS TO PLUMBERS ON JOINT WIPING, PIPE 
BENDING AND LEAD BURNING. Third Edition, 
Revised and Corrected. By John W. Hart, R.P.C. 184 Illus- 
trations. 313 pp. Demy 8vo. Price 7s. 6d. net. (Post frec^ 
8s. Id. home; 8s. 7d. abroad.) 

SANITARY PLUMBING AND DRAINAGE. By 

John W. Hart. Demy 8vo. With 208 Illustt»ations. 250 pp. 
1904. Price 7s. 6d. net. (Post free, 8s. home ; 8s. 2d. abroad.) 

THE PRINCIPLES OP HOT WATER SUPPLY. By 

John W. Hart, R.P.C. With 129 Illustrations. 177 pp. Demy 
8vo. Price 7s. 6d. net. (Post free, 8s. home ; 8s. 2d. abroad.) 

THE PRINCIPLES AND PRACTICE OP DIPPING, 
BURNISHING, LACQUERING AND BRONZ- 
ING BRASS WARE. By W. Norman Brown. 
Revised and Enlarged Edition. Crown 8vo. 48 pp. Price 
3s. net. (Post free, 3s. 4d. hohie and abroad.) 

A HANDBOOK ON JAPANNING. For Ironware, 
Tinware, and Wood, etc. By William Norman Brown. 
Second Edition. Crown 8vo. 70 pages. 13 Illustrations. . Price 
3s. 6d. net. (Post free, 3s. lOd. home ; 4s. Id. abroad.) 

SHEET METAL WORKING. Cutting, Punching^ 
Bending, Folding, Pressing, Drawing and Embossing Metals, 
with Machinery for same. By F. Georgi and A. Schubert. 
Translated from the German. Demy 8vo. 160 pages. 125 Draw- 
ings and Illustrations. 2 Folding Plates. Price 7s. 6d. net. 
(Post free, 8s. home ; 8s. 2d. abroad.) 

(Electric Wiring, etc.) 

THE DEVELOPMENT OP THE INCANDESCENT 
ELECTRIC LAMP. By G. Basil Barham, A.M.I.E.E. 
Demy 8vo. 200 pages. 2 Plates, 25 Illustrations and 10 Tables. 
Price 5s. net. (Post free, 5s. 5d. home ; 5s. 7d. abroad.) 

WIRING CALCULATIONS FOR ELECTRIC 
LIGHT AND POWER INSTALLATIONS. A 
Practical Handbook containing Wiring Tables, Rules, and 
Formulae for the Use of Architects, Engineers, Mining Engineers, 
and Electricians, Wiring Contractors and Wiremen, etc. By G. 
W. LuMMis Paterson. Crown 8vo. 96 pages. 35 Tables. 
Price 5s. net. (Post free, 5s. 4d. home ; 5s. 7d. abroad.) 

ELECTRIC WIRING AND PITTING. By Sydney R 
Walker, R.N., M.I.E.E., M.I.Min.E., A.M.Inst.C.E., etc., etc. 
Crown 8vo. 150 pp. With Illustrations and Tables. Price 5s.. 
net. (Post free, 5s. 4d. home ; 5s. 7d. abroad.) 



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(Brewing and Botanical.) 

HOPS IN THEIR BOTANICAL, AGRICULTURAL 
AND TECHNICAL ASPECT, AND AS AN 
ARTICLE OF COMMERCE. By Emmanuel Gross. 
Translated from the German. 78 lUus. 340 pp. Demy 8vo. Price 
10s. 6d. net. (Post free, lis. Id. home : lis 7d. abroad.) 

INSECTICIDES, FUNGICIDES AND WEED- 
KILLERS. By E. Bourcart, D.Sc. Translated from 
the French. Revised and Adapted to British Standards and 
Practice. Demy 8vo. 450 pages, S3 Tables, and 12 Illustrations. 
Price 12s. 6d. net. (Post free, 13s Id. home ; 13s. 7d: abroad.) 
{For Agricultural Chemistry ^ see p. g.) 

(Wood Products, Timber and Wood Waste.) 

WOOD PRODUCTS: DISTILLATES AND EX- 
TRACTS. By P. Dumesny, Chemical Engineer, 
Expert before the Lyons Commercial Tribunal, Member of the 
International Association of Leather Chemists ; and J. Noybr. 
Translated from the French by Donald Grant. Royal 8vo. 
320 pp. 103 Illustrations and Numerous Tables. Price 10s. 6d. 
net. (Post free, lis. Id home; lis. 7d. abroad.) 

TIMBER : A Comprehensive Study of Wood in all its 
Aspects (Commercial and Botanical), showing the different 
Applications and Uses of Timber in Various Trades, etc. Trans- 
lated from the French of Paul CHARPENTtER. Royal 8vo. 437 
pp. 178 Illustrations. Price 12s. 6d. net. (Post free, 13s. Id. 
home; 14s. Id. abroad.) 

THE UTILISATION OF WOOD WASTE. Trans- 

lated from the German of E. Hubbard. Second Revised English 

Edition. Crown 8vo. 208 pp. 50 lUus. Price 5s. net, (Post 

free, 5s. 5d. home ; 5s. 7d. abroad.) [y^^st published. 

{See also Utilisation of Waste Products ^ p, 9.) 

(Building and Arcliitecture.) 

ORNAMENTAL CEMENT WORK. By Oliver 
Wheatley. Demy 6vo. 83 Illustrations, 128 pp. Price 58. 
net. (Post free, 5s. 5d. home ; 5s. 7d. abroad.) 

THE PREVENTION OF DAMPNESS IN BUILD- 
INGS; with Remarks on the Causes, Nature and 
Effects of Saline, Efflorescences and Dry-rot, for Architects, 
Builders, Overseers, Plasterers, Painters and House Owners. 
By Adolf Wilhelm Keim. Iranslated from the German of the 
second revised Edition by M. J. Salter, F.I.C, F.C.S. Eight 
Coloured Plates and Thirteen Illustrations. Crown 8vo. 115 
pp. Price 5s. net. (Post free, 5s. 4d. home ; 5s. 5d. abroad.) 

HANDBOOK OF TECHNICAL TERMS USED IN 
ARCHITECTURE AND BUILDING, AND THEIR 
ALLIED TRADES AND SUBJECTS. By Auous- 
TINE C. Passmore. Demy 8vo. 380 pp. Price 7s. 6d. net. 
(Post free, 8s. Id. home ; 8s. 7d. abroad.) 

. For contents of these books, see List III. 



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(Foods, Drugs and Sweetmeats.) 

FOOD AND DRUGS. By E. J. Parry, B.Sc, F.I.c!, F.C.S. 
Volume I. The Analysis of Pood and Drugs (Chemical and 

Microscopical). Royal 8vo. 724 pp. Price 21s. net. (Post 

free, 21s. 7d. home ; 22s. 7d. British Colonies; 2ds. 4d. other 

Foreign Countries.) 
Volume II. The Sale of Food and Drugs Acts, 1875-1907. 

Royal 8vo. 184 pp. Price 7s. 6d. net. (Post free, 8s. home ; 

8s. 2d. abroad.) 

THE MANUFACTURE OF PRESERVED FOODS 
AND SWEETMEATS. By A. Hausner. With 
Twent?j(-eight Illustrations. Translated from the German of the 
third enlarged Edition. Second English Edition. Crown 8vo. 225 
pp. Price 7s. 6d. net. (Post free, 7s. lOd. home ; 8s. abroad.) 

RECIPES FOR THE PRESERVING OF FRUIT, 
VEGETABLES AND MEAT. By E. Wagner. 
Translated from the German. Crown 8vo. 125 pp. With 14 
Illustrations. Price 5s. net. (Post free, 5s. 4d. home ; 5s. 5d. 
abroad.) 

(Dyeing Fancy Goods.) 

THE ART OF DYEING AND STAINING MARBLE, 
ARTIFICIAL STONE, BONE, HORN, IVORY 
AND WOOD, AND OF IMITATING ALL SORTS 
OF WOOD. A Practical Handbook for the Use of 
Joiners, Turners, Manufacturers of Fancy Goods, Stick and 
Umbrella Makers, Comb Makers, etc. Translated from the 
German of D. H. Soxhlet, Technical Chemist. Crown 8vo. 
l68 pp. Price 5s. net. (Post free, 5s. 4d. home ; 5s. 5d. abroad.) 

(Celluloid.) 

CELLULOID : Its Raw Material, Manufacture, Properties 
and Uses. A Handbook for Manufacturers of Celluloid and 
Celluloid Articles, and all Industries using Celluloid ; also for 
Dentists and Teeth Specialists. By Dr. Fr. B6ckmann, Tech- 
nical Chemist. Translated from the Third Revised German 
Edition. Crown 8vo. 120 pp. With 49 Illustrations. Price Ss. 
net. (Post free, 5s. 4d. home ; 5s. 5d. abroad.) 

(Lithography, Printing and 
Engraving.) 

ART OP LITHOGRAPHY. By H. J. Rhodes. Demy 
8vo. 344 pages. 120 Illustrations. 2 Folding Plates. Copious 
combined Index and Glossary. Price 10s. 6d. net. (Post free, 
lis. Id. home ; lis. 4d. abroad.) 



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PRINTERS' AND STATIONERS' READY 
RECKONER AND COMPENDIUM. Compiled by 
Victor Graham. Crown 8vo. 1 12 pp. 1904. Price 3s. 6d. net. 
(Post free, 3s. lOd. home ; 4s. abroad. ) 

ENGRAVING FOR ILLUSTRATION. HISTORI- 
CAL AND PRACTICAL NOTES. By J. Kirkbridb. 
72 pp. Two Plates and 6 Illustrations. Crown 8vo. Price 
2s. 6d. net. (Post free, 2s. lOd. home ; Ss. abroad.) 
{For Printing Jnks^ see p, 4.) 

(Bookbinding.) 

PRACTICAL BOOKBINDING. By Paul Adam. 
Translated from tne German. Crown 8vo. 180 pp. 127 Illus- 
trations. Price 5s. net. (Post free, 5s. 5d. home ; 5s. 7d. abroad.) 

(Sugar Refining.) 

THE TECHNOLOGY OP SUGAR: Practical Treatise 
on the Modern Methods of .Manufacture of Sugar from the Sugar 
Cane and Sugar Beet. By John Geddes McIntosh. Third Edi- 
tion, Revised and Enlarged. Demy Svo. 540 pages. 244 Illustra- 
tions. Price 12s. 6d. net. (Post free, 13s. Id. home ; 13s. 9d. abroad.) 

[Just published, 
(See ** Evaporating, Condensing, etc.. Apparatus,'* p. i8.) 

(Emery.) 

EMERY AND THE EMERY INDUSTRY. Trans- 
lated from the German of A. Haenig. Crown Svo. 45 Illus. 
104 pp. Price 5s. net. (Post free, 5s. 4d. home ; 5s. 7d. abroad.) 

(Bibliography.) 

CLASSIFIED GUIDE TO TECHNICAL AND COM- 
MERCIAL BOOKS. Compiled by Edgar Green- 
wood. Demy Svo. 224 pp. 1904. Being a Subject-list of the 
Principal British and American Books in Print; giving Title, 
Author, Size, Date, Publisher and Price. Price 5s. net. (Post 
free, 5s. 5d. home ; 5s. 7d. abroad.) 

HANDBOOK TO THE TECHNICAL AND ART 
SCHOOLS AND COLLEGES OF THE UNITED 
KINGDOM. Containing particulars of nearly 1,000 
Technical, Commercial and Art Schools throughout the United 
Kingdom. With full particulars of the courses of instruction, 
names of principals, secretaries, etc. Demy Svo. 150 pp. Price 
3s. -ed. net. (Post free, 4s. home ; 4s. Id. abroad.) 

SCOTT, GREENWOOD & SON, 

TECHNICAL BOOK. AND TRADE JOURNAL PUBLISHERS, 
8 BROADWAY, LUDGATE, LONDON, EX. 

Telegraphic Address, •• Printeries, Cent., London ". December, 1915. 

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